Drought a prolonged, continuous period of dry weather along with abnormal insufficient rainfall. It occurs when evaporation and transpiration exceed the amount of precipitation for a reasonable period. Drought causes the earth to parch and a considerable hydrologic (water) imbalance resulting water shortages, well to dry, depletion of  soil moisture, stream flow reduction, crops to wither leading to crop failure and scarcity in fodder for livestock. Drought is a major hazard faced by communities directly dependent on rainfall for drin-king water, crop production, and rearing of animals. Droughts are common in the northwestern districts of Bangladesh. Due to drought severity, crop loss ranges between 20 and 60 percent or even may be more for transplanted aman and other rice varieties. Depending on the intensity of drought, the estimated yield reduction of different crops varies from 10% to 70%. According to Bangladesh Meteorological Department, “There was 21 per cent less rain during the monsoon period from June to August in 2009 and the northern districts suffer from drought”. Drought is one of the key natural disasters in Bangladesh (Omer, 2008). It has become a major concern in the country, particularly in terms of Bangladesh agricultural production and environmental damage. It adversely impacts agricultural production and natural environment, mostly areas in the north-western part. Meteorological drought is defined on the basis of the degree of dryness and the severity of drought in a region. For instance, annual rainfall between 25% and 50% deficiency was considered as moderate drought whereas annual rainfall less than the value of 50% deficiency was considered as severe drought in a region. Moreover, a year was considered as a drought year when the total area of the country was affected individually with more than 20% deficiency of annual rainfall. Bangladesh has experienced drought frequently over the past years (Murad et al., 2011; Muna et al., 2023; Hossain et al., 2023). 

However, drought should be assessed importantly to understand its magnitude in different areas (Sirdaş and Şen, 2003) from the past meteorological records. Meteorological information, particularly regional rainfall evidence (Patel et al., 2007), is the common way of drought diagnosis by using GIS technique (Chopra, 2006). Spatially explicit drought conditions may offer valuable concerns through this technique (Eriyagama et al., 2009), which needs to be applied in case of Bangladesh drought assessment. Several studies have been carried out on droughts and related issues in Bangladesh (Solomon, 2007). Most of the researches in Bangladesh are mainly on agricultural drought and region-based (Alam et al., 2011). For instance, a study conducted by Alam et al. (2014) showed the spatial extent of agricultural drought in Barind regions of Bangladesh by using statistical measure. Spatiotemporal extent of drought was also analyzed by Akter and Rahman (Akter and Rahman, 2012) which indicated the adverse impact of shortage of seasonal rainfall and its consequences on drought by using Rainfall Anomaly Index (RDI).

Rainfall is the primary factor governing the development and persistence of the drought Phenomenon. Therefore, the assessment of patterns and trends of rainfall was conducted in this study. Trend analysis was carried out using a non-parametric MK test. It is a widely used test for its suitability for non-normally distributed data and censored data. The continuous wavelet transform is an important tool to study variations of variables like rainfall (Kun et al., 2012). 

Yearly drought analysis was performed by three climatic indices. The climatic indices are De Mortone Aridity Index (IdM), Seleaninov Hydrothermic Index (IhS), and Donciu Climate Index (IcD). Jahangir et al. (2013) used SPI to evaluate the precipitation deficit, and Markov chain model was used to quantify the drought in agricultural extent. According to Mishra and Desai, (2005), 2–3 months period of SPI may indicate agricultural drought best. It also reflects short-term moisture conditions of soil. When exploring the cause of droughts, a climatic index may be provided by a coupled atmosphere-ocean system, which may be used to control precipitation. For example, the El Nio-Southern Oscillation (ENSO) phenomenon, which took place in the tropical Pacific, impacted areas beyond the tropical regions with hydro-meteorological disasters like floods and droughts. The other factors affect droughts are sea surface temperature, deforestation, over exploitation of resources, rising level of CO2 and greenhouse gases etc. This is why droughts and fresh water shortages may be considered as a factor which increases the gap between developed and developing countries (Prokurat, and Sergiusz, 2015). The effect varies according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food sources. Areas with populations that depend on water sources as a major food source are more vulnerable to famine.

Statement of the Problem

Rainfall data is considered an important parameter for studying water resources related problems like flood which is a common phenomenon in Bangladesh. However, developing a rainfall forecasting model is a challenging task considering the technical and political circumstances. Technical problems arise from the lack of ground-based rainfall measuring equipments such as radar network or automated raingauges. The solution to overcome these problems lies on the use of satellite based remote sensing devices. In and around Bangladesh, the rainy season is divided into three periods: (a) pre-monsoon (March-May), (b) monsoon (June-September), and (c) post-monsoon (October-November). In Bangladesh, about 20%, 62.5%, 15.5%, and 2% of the annual rainfall (~2700 mm) occurs during pre-monsoon, monsoon, post-monsoon, and winter periods, respectively (Islam & Uyeda, 2005).

Scope of the Research

Drought is a natural phenomenon. We cannot avoid drought. But we can reduce the impact of drought on people, agriculture and livelihood activities of human. In this research I tried to understand the intensity and cumulative probability of drought occurrence in 2009 on the northern Bangladesh. Using drought indices we can easily see the probability of drought. We should monitor drought to determine the current status of specific resources, detect changes and long-term trends and obtain knowledge of fundamental linkages and processes at work Enable development and implement-ation of early warning indicators. Combination of climate, soil, and water data, local and regional coverage Impact assessments and drought Indices are needed to monitor drought.

Aim and Objectives of the research

• To investigate more about drought, available tools to classify and forecast drought; 
• To  explore the drought monitoring indices and its application procedures;
• To determining drought scenarios in the case on Rangpur and Nilphamary Districts at 2009. 

Research Question

To fulfill my research I have a research question:-

Why should we monitor drought?

The Research Gap explains the logic of conducting the next research. To fulfill my research work I have taken help from the following literature review. Though these are not exactly related to my topic I have been benefited in a great extent. The literature review of my research is given below. Shamsuddin Shahid, (2014) - Spatial and temporal characteristics of droughts in the western part of Bangladesh has been analysed. Analysis of seasonal rainfall distribution, rainfall reliability and long-term rainfall trend is also conducted to aid prediction of future droughts in the area. Mondol et al. (2016) - Natural disasters are a major concern in Bangladesh, particularly drought which is one of the most common disaster in Bangladesh. We used rainfall data of 30 meteorological stations in Bangladesh during the study period of 1981–2010. The results indicate that drought has been fluctuating and it has become a recurrent phenomenon during the study period. 

Nury. A. H., Hasan. K. (2015) - the study explored droughts using the Standardized Precipitation Index (SPI) in the northwestern region of Bangladesh, which is the drought prone area. The outcomes from this study contribute to hydrologists to establish strategies, priorities and proper use of water resources. Monacelli et al. (2005) - The fight against drought and desertification receives a high priority in the Long-term Plan of the World Meteorological Organization (WMO), particularly under the Agricultural Meteorology Programme, the Hydrology and Water Resources Pro-gramme and the Technical Co-operation Programme. Furthermore, WMO continues to actively involve the National Meteorological and Hydrological Services (NMHSs) and the regional and sub-regional meteorological centres and intensify research on the interactions between climate, the hydrological regime and desertification.

M. G. Ferdous and M. A. Baten, (2011) - An agro-climatic study was conducted at three regions of Rajshahi division with 50 (1961-2010) years of climatic data (temperature, rainfall, relative humidity and sunshine) to observe the climatic variability. Average relative humidity was showed increasing trends over Rajshahi, and Dinajpur region by 0.0261, and 0.0269%/year. Over Rangpur region, the decreasing trend was observed by 0.0599%/year. Emre et al. (2009) - Drought is a vital phenomenon in semi-arid regions; particularly in endorheic (closed) basins where water resources are scarce to meet demands. Konya Closed Basin is one of the most susceptible basins to drought in Turkey. Islam et al., (2015) - The 1994, 2000 and 2006 drought appeared to bad memories in the northern region of Rangpur division, Bangladesh. The results revealed that drought were adversely impacted on social and agro-ecology in the study area. It is suggested that if awareness and literacy level increases to diminish social and agro-ecological impact of drought in the study area.

Rakib et al., (2015) - Drought is the most formidable disaster frequently reoccurring in most regions of Bangladesh. It is a natural slow onset hazard which evolves unnoticed and enhancing due to the onslaught of global climate change. Aim is to minimize the impact of drought for enhanced sustainability of growth in the agricultural sector and socioeconomic life of Bangladesh and other countries in similar conditions. Chang-Soo Rim, (2012) - The implications of geographical factors (i.e. elevation, freshwater area, urbanization, and proximity to coast) and climatic factors with regard to drought trend were investigated by analyzing the monthly averaged daily climate data recorded from 1973 to 2006 at 53 climatological stations in South Korea. Therefore, for efficient water resources management for drought preparedness, drought duration and seasonality should also be considered along with geographical and climatic characteristics of a region.

Siegfried et al., (2016) - Drought affects virtually every region of the world, and potential shifts in its character in a changing climate are a major concern. This article presents a synthesis of current understanding of meteorological drought, with a focus on the large-scale controls on precipitation afforded by sea surface temperature (SST) anomalies, land surface feedbacks, and radiative forcings. Islam. S, and Islam. N, (2006) - In recent years, rainfall estimation from remotely sensed data has been considered a viable alternative over the traditional rain-gauge measurements. In this report, daily rainfall data with one degree resolution measured by Tropical Rainfall Measuring Mission (TRMM) satellite with the 3B42 processing algorithm has been used to quantify the precipitation over Bangladesh. The average percentage of rainy days determined by TRMM data with respect to the rain-gauge value was 96%. Mbugua. A, (2011) - Gram Bikash Kendra, GBK, is an NGO operating in North West of Bangladesh in five districts. Its scope of work is with marginalized and vulnerable people including Dalits, Indigenous people and the ultra-poor people, to uplift their conditions of life. The main stakeholders are GBK, VSOB, Department of Agricultural Extension, the community in general, Shallow tube machine owners and businessmen, teachers, Union Parishad members, farmers and NGOs.

Faroque et al., (2015) - Climate change is no more an environmental concern it has emerged as biggest developmental challenge for the most vulnerable Bangladesh. This paper tries to focus the adverse impacts of climatic changes on the crop production, food security, yield gap and diversification. Also need top priority to mitigate the impact of climate change on agriculture through weather services, more research and management technologies for future sustainable agriculture. Paul et al., (2013) - The objective of this paper is to explore people's survival strategies and coping capacities to combat monga at household level in the northern region of Bangladesh. The present study argues that the policy makers of Government and NGOs should emphasize on enhancing of coping capacities of poor and and agro-based industrialization in the northern Bangladesh. Zoltán Dunkel, (2009) - The paper summarizes the indices used for identification of drought phenomenon in the agricultural meteorology practice. The discussion on drought definition together with the survey of the indices tries to highlight the wide possible categorization of this very important phenomenon mainly from the meteorological point of view.

Study Area

Rangpur District: Rangpur district was established in 1772. Nothing is definitely known about the origin of the district name. It is said that a representative of Banglar Nawab named Badarjung had a Rang Mahal (meaning house of enjoyment) in this area. The other opinion is that the king of Kamrup had built a Rang Mahal in this area for amusement. This might be the origin of the district name to be Rangpur. The district is bounded on the north by Nilphamari and Lalmonirhat districts, on the east by Lalmonirhat, Kurigram and Gaibandha districts, on the south by Gaibandha and Dinajpur districts and on the west by Dinajpur and Nilphamari districts with an area of 2400.56 sq km. The district lies between 25º18˝ and 25º57˝ north latitudes and between 88º56˝ and 89º32˝ east longitudes.

Fig. 1: Rangpur and Nilphamari District.

Nilphamari District: Nilphamari is a district in Northern Bangladesh. It is a part of the Rangpur Division. It is 400 km from the capital Dhaka in north and west side. It has an area of 1,547 square kilometres (597 sq mi). Nilphamari is recently marked as edu-cation district as it has highest education level in Bangladesh. Nilphamari is bounded by Rangpur and Lalmonirhat in east, Rangpur and Dinajpur in south, Dinajpur and Panchagarh in west, Siliguri of India in north.

Palmer Drought Severity Index (PDSI) 

The PDSI is based on precipitation and temperature data, on the local Available Water Content (AWC) of the soil and other meteorological parameters. The Palmer Index has been widely used but it has some limitations. Among these we mention: the index is highly sensitive to the AWC of a soil type and that there are some difficulties in comparing the results obtained in regions with different water balances. The Palmer Drought Severity Index (PDSI) uses readily available temperature and precipitation data to estimate relative dryness. It is a standardized index that spans -10 (dry) to +10 (wet). It has been reasonably successful at quantifying long-term drought. As it uses temperature data and a physical water balance model, it can capture the basic effect of global warming on drought through changes in potential evapotranspiration. Monthly PDSI values do not capture droughts on time scales less than about 12 months; more pros and cons are discussed in the Expert Guidance. The Palmer Index varies between -6.0 and +6.0. The index classification is shown in the following table:

Table 1: PDSI Classification.

To quantify drought and monitor its development, many drought indices have been developed and applied. Among them, the Palmer Drought Severity Index (PDSI) is the most prominent index of meteo-rological drought used in the United States for drought monitoring and research, and its variants have been used to quantify long-term changes in aridity over land in the 20th  and 21st  century. The PDSI has also been widely used in tree-ring based reconstructions of past droughts in North America and other regions. The standardization used by Palmer was based on limited data from the central U.S. and tends to yield more severe PDSI in the Great Plains than other U.S. regions.

Another major complaint about the PDSI is that the PE calculated using the Thornthwaite equation in the original Palmer model could lead to errors in energy-limited regions Hobbins et al., (2008), as the Thornthwaite PE (PE_th) is based only on temperature, latitude and month. The PDSI is also imprecise in its treatment of all precipitation as immediately available rainfall (i.e., no delayed runoff from melting snow), its lack of impact of vegetation or frozen soils on evaporation, and some other processes. Despite all these caveats, Dai et al. (2004) and Dai, (2011) showed that the PDSI values are significantly correlated with measured soil moisture content in the warm season and streamflow over many regions over the world, and satellite observed land water storage changes, and  these correlations are comparable over the U.S. and many other parts of the world. This suggests that the PDSI can be used as a measure of drought over land, especially over the low and middle latitudes. 

The effect of global warming may have already occurred during the 20th century Dai et al., (2004); van der Schrier et al., (2006), Dai, (2011) and may increase substantially  in the 21st century Burke and Brown, (2008); Dai, (20110. The effect of surface temperature, which accounts for 10-30% of PDSI's variance during the 20th century, comes mainly through potential evapotranspiration. As precipitation and surface air temperature are the only two climate variables with long historical records, the PDSI makes full use of these data and can be readily calculated for the last hundred years or so for most land areas. The impact of the choice of PE_th or PE_pm is relatively small for the 20th century, the use of PE_th tends to overestimate the impact of the globalwarming for the model-projected 21st century climate. Dai, (2011, JGR) compared the various versions of the PDSI and recommended the use of the sc_PDSI with the PE_pm (i.e., sc_PDSI_pm), especially for model projections.

Standardized Precipitation Index (SPI)

The climate of a region is determined by the long-term average, frequency and extremes of several meteo-rological variables, most notably temperature and precipitation. Precipitation is a precious natural resource and it is quite variable. Thus any fluctuations or trends in its geographical distribution and quantity could have significant implications for socioeconomic sectors such as agricultural productivity, food security, water quality, water resource management, land use, human health, as well as ecological impacts such as biodiversity. Therefore, it is essential to derive regionally consistent precipitation zone maps for use in a variety of practical applications and in climate impact research. 

Some applications of the SPI

Researchers have employed SPI to examine numerous questions such as, drought, teleconnections with large scale circulatory systems, floods and crop yields. El Niño Southern Oscillation (ENSO) phenomenon has been related to several weather and climatic extremes around the world. Fernández and Fernández, (2002) identified several zones in the continental region of southern South America, where teleconnections exist between the extreme phases of ENSO and precipitation zones characterized through the use of SPI. Seiler et al. (2002) used SPI to study the recurrent floods affecting the southern Córdoba Province in Argentina, as a tool for monitoring flood risk in that region. SPI satisfactorily explains the development of conditions leading up to the three main flood events in the region during the past 25 years. They proposed applying SPI as an effective tool for a regional climate risk monitoring system. Sims et al. (2002) compared PDSI and SPI for estimating soil moisture in the western mountains, central piedmont, and the coastal plain in North Carolina, USA. Results suggest SPI to be more representative of short-term precipitation and soil moisture variation and hence a better indicator of soil wetness. Anctil et al. (2002) conducted a regional analysis of 5-day precipitation and demonstrated that SPI can be used beyond its usual diagnostic function, by quantifying the probability that precipitation to come will put an end to an ongoing drought. Crop rotation is used worldwide to improve farming practice. The positive attributes of rotations are usually dependent upon crop choices, cropping sequence, soil fertility management, and weather factors. Regression of yield as the dependent variable and the 12-month April SPI as the independent variable explained up to 64% of yield variability in a curvilinear relationship. Used with other criteria, the SPI can be a practical guide to choice of crops, N levels, and management decisions to conserve water in rain-fed systems.

Standardized Precipitation Index (SPI) Calculation

The SPI was developed by McKee et al (1993). It was designed to quantify the precipitation deficit for mul-tiple time scales. These time scales reflect the impact of a drought on the availability of the different water resources. Soil moisture conditions respond to precipitation anomalies on a relatively short scale. Groundwater, streamflow, and reservoir storage reflect the longer-term precipitation anomalies. For these reasons, McKee et al. (1993) originally calculated the SPI for 3, 6, 12, 24, and 48 month time scales. The calculation of the index needs only precipitation record. It is computed by considering the precipitation anomaly with respect to the mean value for a given time scale, divided by its standard deviation. The precipitation is not a normal distribution, at least for time-scales less than one year. Therefore, the variable is adjusted so that the SPI is a gaussian distribution with zero mean and unit variance. A so adjusted index allows comparing values related to different regions. Moreover, because the SPI is normalized, wet and dry climates can be monitored in the same way. The index calculation is based on the following expressions: 

Where P is the cumulated precipitation for the given time-scale, H(P) is the cumulative probability of the observed precipitation and c0, c1, c2, d1, d2, d3 are mathematical constants. The classification shown in the following table is used to define drought intensities resulting from the SPI computation:

Sources of Data

Data source is very important for any kind of research. Accurate and enough data is the pre requisite to fulfill the research. In my research I have collected the data related to my research objectives from two sources: such as

• Primary Sources of Data

• Secondary Sources of Data

Primary Sources of Data

The Primary Sources of Data related to my research topic are directly related to the field survey. Various Primary Sources of Data are used in my research. These are mentioned below.

Secondary Sources of Data

Secondary Sources of Data are mainly the published and unpublished books, journals etc. In my research I have followed the below mentioned secondary sources.

Books

Different kinds of books of the different authors related to my research I have followed. Though in this book I have not got my topics exactly but I have been benefited in a great extent.

Journals

To complete my research work I have taken help from several journals and publications which have been published from the different source.

Reports

I have followed several reports related to my res-earch work.

Newspaper

Newspaper is the source of all knowledge. To complete my research I have read the different kind of column published in the different kinds of newspaper in the different time.

Internet

For the development of the technologies the difficult work has become easier and time saving. To complete my research I have got helped from the internet. I have updated my information from the internet. To achieve my goal I have to visit in the different website.

Articles

Different kinds of articles of the different authors related to my research I have followed. Though in this article I have not got my topics exactly but I have been benefited in a great extent. The impact of droughts was higher in the western part of the country compared to other parts. In recent decades, the hydro-climatic environment of north-western Bangladesh has been aggravated by environmental degradation and cross- country anthropogenic interventions (Bangla-pedia, 2006). Scientists have become increasingly concerned about the frequent occurrence of drought in western districts of Bangladesh, and this paper reports on studies of drought conditions in the western part of Bangladesh.

Drought definition 

The available water over land has, fundamentally, an atmospheric source (cyclic water). In the table some estimates of the volumes for the available water are shown:

Table 2: Some estimates of the volumes for the available water.

An annual mean precipitation estimate is around 0.5 106 km3.This value is forty-times as big as the water present in the atmospheric average. Therefore, a total recharge of the atmospheric water occurs in a short period (around 9 days). In the study of the hydrological cycle, these processes are of primary relevance leading to the the final result, i.e. the precipitation, which must be diagnosed in a climatological context. The occurrence of dry and wet periods is a feature of the natural variability of the hydrological cycle. It manifests itself in different time and space scales and it produces several impacts on society. The word "Drought" is often associated with different meanings. Therefore, it is worth explaining the fundamental aspects about the concept of drought in a hydrometeorological context.

Drought in Northwest Bangladesh

In Bangladesh, three types of droughts are recognized during monsoon season: early-season, mid-season and terminal-season droughts. Irrigated agricultural areas alongside the rivers in Bangladesh may experience a hydrological drought as a result of low rainfall. Also, Barind areas that use deep or shallow boreholes to draw water from underground aquifers may experience hydrological drought as well because of geological changes that cut off parts of the aquifers. Thus, Northwestern regions are particularly vulnerable to droughts. Apart from loss to agriculture, droughts have significant effect on land degradation, livestock population, employment and health.

History and Current Scenario of Drought

Between 1960 And 1991, Droughts Occurred In Bangladesh 19 Times. Very Severe Droughts Hit The Country In 1951, 1961, 1975, 1979, 1981, 1982, 1984, 1989, 1994, 1995 And 2000. Past Droughts Have Typically Affected About 47 Percent of the Country and 53 Percent of The Population. The Drought Of 1979 Was One of The Severest In Recent Times. 

Chronology of droughts of historical significance

1791- Drought affected Jessore district. Prices had risen to twice and three times of their usual levels.

1865- Drought proceeding famine occurred in Dhaka.

1866- Severe drought in Bogra. The rice production of the district was hit hard and the price went up three times its normal level.

1872- Drought in Sundarbans. The rainfall was deficient and in several lots the crops suffered to a great extent.

1874- Bogra was affected and the crop failure was much greater. The rainfall was extremely low.

1951- Severe drought in northwest Bangladesh and substantially reduced rice production.

1973- One of the severest in the present century and was responsible for the 1974 famine in northern Bangladesh.

1975- This drought affected 47% of the entire country and caused sufferings to about 53% of the total population.

1978-79- Severe drought causing widespread damage to crops. 

1981- Severe drought adversely affected crop production.

1982- Caused a total loss of rice production amounting to about 53,000 tons. In the same year flood damaged about 36,000 tons of rice.

1989- Most of the rivers in NW Bangladesh dried up and several districts.

1994-95- This drought was followed by that of 1995-96, caused immense damage to crops, especially in the case of rice and jute the main crops of NW Bangladesh. 

Fig. 2: Physiological activity of Drought during Time.

The region faced extreme drought during the year 1994, marked as the driest year in the contemporary periods. The drought that occurred in 1994, particularly with a severe out-break in the north-western part of the country has left the people in an insecure condition. The situation turned worse due to abnormally low level of rainfall, which caused drying up of surface water bodies like canals, ponds, beels, and rivers in the region. The irrigation system was under severe stress as most of the shallow and hand tube wells (HTW) went dry and posed a serious threat to food grain production. The groundwater level declined to an abnormally low level compared Drought mostly affects Bangladesh in premonsoon and post-monsoon periods. From 1949 to 1979 drought conditions had never affected the entire country. The percentage of drought affected areas were 31.63% in 1951, 46.54% in 1957, 37.47% in 1958, 22.39% in 1961, 18.42% in 1966, 42.48% in 1972 and 42.04% in 1979. During 1981 and 1982 droughts affected the production of the monsoon crops only. During the last 50 years, however, Bangladesh suffered about 20 drought conditions. The drought condition in North-western Bangladesh in recent decades had led to a shortfall of rice production of 3.5 million tons in the 1990s. If other losses, such as, to other crops (all rabi crops, wheat, sugarcane, tobacco, etc.) as well as to perennial agricultural resources, such as, bamboo, betel nut, fruits like litchi, mango, jackfruit, banana, etc. are considered, the loss is substantially much higher.

Causes of Drought

Causes of drought in Bangladesh are related to climate variability and nonavailability of surface water resources. While it may be possible to indicate the immediate cause of a drought in a particular location, it often is not possible to identify an underlying cause. Some of the causes for drought in northern Bangladesh have been explained as follows:

• Climatic or Weather Conditions: The immediate cause of a rainfall shortage may be due to one or more factors including absence of moisture in the atmosphere or large-scale downward movement of air within the atmosphere which suppresses rainfall. 
• Uneven Distribution of Rainfall: The scarcity of water in these areas has also been exacerbated by the low and uneven distribution of rainfall in recent years due to the effects of climate change. 
• Internationally Shared Waterways: Another main reason for the drought situation is the internationally shared waterways. The hydrological and climatic conditions of Bangladesh are already characterized by too much water in the wet monsoon and too little in the dry months. The drought environment is further aggravated by the cross boundary anthropogenic interventions.
• Overexploitation of groundwater: Besides, due to lack of proper knowledge and non-availability of modern technologies, farmers inappropriately lift water without caring ground sources and hence water table declines in many areas of Bangladesh. 
• Physical Factors: Drought conditions are further aggravated by non-availability of deep tube wells, low moisture retention capacity of the soil, highly variable rainfall and low adaptive capacity of farmers.

Impacts of drought in Bangladesh 

Every five years, Bangladesh is affected by the major country-wide droughts. However, local droughts occur regularly and affect crop production. The agricultural drought, linked to soil moisture scarcity, occurs at different stages of crop growth, development and reproduction. Monsoon failure often brings famine to the affected regions and as a result crop production reduces drastically. Northwestern regions of Bangladesh are particularly exposed to droughts. A strong drought can cause greater than 40% damage to broadcast aus. During the kharif season, it causes significant destruction to the t. aman crop in approximately 2.32 million ha every year. In the rabi season, about 1.2 million ha of agricultural land face droughts of different magnitudes. Apart from the agricultural loss, droughts have important effect on livestock population, land degradation, health and employment. Between 1960 and 1991, drought events occurred 19 times in Bangladesh. Very strong droughts hit the country in 1961, 1975, 1981, 1982, 1984, 1989, 1994, and 2000. Past droughts have naturally affected about 53% of the population and 47% of the country. 

The region faced extreme drought during the year 1994, marked as the driest year in the contemporary periods. The drought that occurred in 1994, particularly with a severe out-break in the north-western part of the country has left the people in an insecure condition. The situation turned worse due to abnormally low level of rainfall, which caused drying up of surface water bodies like canals, ponds, beels, and rivers in the region. The irrigation system was under severe stress as most of the shallow and hand tube wells (HTW) went dry and posed a serious threat to food grain production. The groundwater level declined to an abnormally low level compared Drought mostly affects Bangladesh in premonsoon and post-monsoon periods. From 1949 to 1979 drought conditions had never affected the entire country. The percentage of drought affected areas were 31.63% in 1951, 46.54% in 1957, 37.47% in 1958, 22.39% in 1961, 18.42% in 1966, 42.48% in 1972 and 42.04% in 1979. During 1981 and 1982 droughts affected the production of the monsoon crops only. During the last 50 years, however, Bangladesh suffered about 20 drought conditions. The drought condition in North-western Bangladesh in recent decades had led to a shortfall of rice production of 3.5 million tons in the 1990s. If other losses, such as, to other crops (all rabi crops, wheat, sugarcane, tobacco, etc.) as well as to perennial agricultural resources, such as, bamboo, betel nut, fruits like litchi, mango, jackfruit, banana, etc. are considered, the loss is substantially much higher.

Causes of Drought

Causes of drought in Bangladesh are related to climate variability and nonavailability of surface water resources. While it may be possible to indicate the immediate cause of a drought in a particular location, it often is not possible to identify an underlying cause. Some of the causes for drought in northern Bangladesh have been explained as follows:

• Climatic or Weather Conditions: The immediate cause of a rainfall shortage may be due to one or more factors including absence of moisture in the atmosphere or large-scale downward movement of air within the atmosphere which suppresses rainfall. 
• Uneven Distribution of Rainfall: The scarcity of water in these areas has also been exacerbated by the low and uneven distribution of rainfall in recent years due to the effects of climate change. 
• Internationally Shared Waterways: Another main reason for the drought situation is the internationally shared waterways. The hydrological and climatic conditions of Bangladesh are already characterized by too much water in the wet monsoon and too little in the dry months. The drought environment is further aggravated by the cross boundary anthropogenic interventions.
• Overexploitation of groundwater: Besides, due to lack of proper knowledge and nonavailability of modern technologies, farmers inappropriately lift water without caring ground sources and hence water table declines in many areas of Bangladesh. 
• Physical Factors: Drought conditions are further aggravated by nonavailability of deep tube wells, low moisture retention capacity of the soil, highly variable rainfall and low adaptive capacity of farmers.

Impacts of drought in Bangladesh 

Every five years, Bangladesh is affected by the major country-wide droughts. However, local droughts occur regularly and affect crop production. The agricultural drought, linked to soil moisture scarcity, occurs at different stages of crop growth, development and reproduction. Monsoon failure often brings famine to the affected regions and as a result crop production reduces drastically. Northwestern regions of Bangladesh are particularly exposed to droughts. A strong drought can cause greater than 40% damage to broadcast aus. During the kharif season, it causes significant destruction to the t. aman crop in approximately 2.32 million ha every year. In the rabi season, about 1.2 million ha of agricultural land face droughts of different magnitudes. Apart from the agricultural loss, droughts have important effect on livestock population, land degradation, health and employment. Between 1960 and 1991, drought events occurred 19 times in Bangladesh. Very strong droughts hit the country in 1961, 1975, 1981, 1982, 1984, 1989, 1994, and 2000. Past droughts have naturally affected about 53% of the population and 47% of the country. 

Agricultural Impact

Drought is one of the major environmental stresses in the north that drastically limits the grain yield of rice, a staple food of Bangladeshi people. This causes a lot of people to become unemployed and fall into acute food shortage between late July and early November. During this interim period, there are no alternative agricultural activities left for people and the small non-agricultural sector cannot absorb the seasonally unemployed labour force. Climate change would also alter crop water requirement in drought-prone Bangladesh. The highest crop water needs are in hot, dry, windy and sunny seasons (November-May). 

The lowest needs occur when it is cool, humid and cloudy with little wind. It is clear that crops grown in current and future climatic conditions will have different water needs. For example, rice grown in the future will need more water per day. Of the net cultivable area, 37 percent is single cropped, 50 percent is double cropped and 13 percent is triple cropped. The three cropping seasons coincide approximately with the three meteorological seasons namely, kharif I (pre-monsoon), kharif II (monsoon) and rabi (dry season). Aus, aman and boro are the three rice crops grown in these three cropping seasons respectively. In the Barind tracts of Northwest Bangladesh, t. aman rice grown during monsoon and boro rice during rabi (winter) are prone to drought. Soil moisture generally remains low during the winter season (dry period) in Bangladesh. However, farmers grow winter crops (e.g., vegetables, boro rice, etc.) in an incremental rate mostly depending on the availability of groundwater to satisfy its demand. 

Monsoon rainfall has a direct effect on groundwater recharge. Due to low rainfall in 1994 winter season experienced a lowering of water table below pumping suction level. The predominantly shallow tubewell zones of northwest region of Bangladesh fell short of supplying its irrigation requirement from the underground source. Under the situation, it is of particular interest to assess the groundwater deficit prevailed in that winter season. It focuses mainly on the availability of dependable water resources in the aforesaid area with regards to supply for irrigation requirement. 

Fig. 4: Agricultural Impact of Drought (Source: climatechange.org.bd).

Agricultural drought, linked to soil moisture scarcity, occurs at different stages of crop growth, development and reproduction. Monsoon failure often brings famine to the affected regions and as a result crop production reduces drastically. A severe drought can cause more than 40 percent damage to broadcast aus. During the period of 1973-87, about 2.18 million tons of rice was damaged due to drought, while the extent of crop loss was 2.38 million tons due to flood in the same period (Paul, 2013). Drought normally affects about 2.3 million ha of cropland from April to September and 1.2 million ha in the dry season, from October to March. Drought during monsoon season severely affects t.aman rice and can incur an annual 1.5 million tonne production loss. With climate change, more area would be exposed to severe droughts because of projected change in rainfall pattern and dry spell frequencies. Drought affects not only the seasonal crops but also the fruit-bearing trees, forestry and the environment as a whole. Moreover, the crop environment during the monsoon (Kharif-II) season is not favourable for achieving full potential yields because of uneven distribution of rainfall, flooding, etc. 

The scope of increasing the irrigation areas by LLP is limited. In this circumstances, there is no option but to use surface water to meet the water deficit created by droughts in the Kharif-II season and hence, surface water utilization projects such as barrages across the rivers, installation of pumping plants for lifting water from the rivers are essential.

Agricultural drought, linked to soil moisture scarcity, occurs at different stages of crop growth, development and reproduction. Monsoon failure often brings famine to the affected regions and as a result crop production reduces drastically. A severe drought can cause more than 40 percent damage to broadcast aus. During the period of 1973-87, about 2.18 million tons of rice was damaged due to drought, while the extent of crop loss was 2.38 million tons due to flood in the same period (Paul, 2013). Drought normally affects about 2.3 million ha of cropland from April to September and 1.2 million ha in the dry season, from October to March. Drought during monsoon season severely affects t.aman rice and can incur an annual 1.5 million tonne production loss. With climate change, more area would be exposed to severe droughts because of projected change in rainfall pattern and dry spell frequencies. Drought affects not only the seasonal crops but also the fruit-bearing trees, forestry and the environment as a whole. Moreover, the crop environ-ment during the monsoon (Kharif-II) season is not favourable for achieving full potential yields because of uneven distribution of rainfall, flooding, etc. 

The scope of increasing the irrigation areas by LLP is limited. In this circumstances, there is no option but to use surface water to meet the water deficit created by droughts in the Kharif-II season and hence, surface water utilization projects such as barrages across the rivers, installation of pumping plants for lifting water from the rivers are essential.

The associated decline in crop production, losses of assets and lower employment opportunities contributed to increased household food insecurity. It has been predicted that by 2018, the demand for irrigation may reach 58.6 percent of the total supply. The demand for other sectors is expected to reach 40.7 percent for inland waterway navigation, salinity management and fisheries, and 0.7 percent for domestic and industrial use. The Bangladesh agriculture sector contributes about 30 percent to its gross domestic product (GDP). Nearly 75 percent of the population is directly or indirectly dependent on agriculture. Its share of water demand will continue to increase, concurrent with efforts to attain food security within the crop sector, food grains, particularly rice, dominate the country's agricultural scenarios in both cropped area and production, claiming a share of 77 percent in 2000. During the past two decades, the area under boro rice has increased – a trend that is likely to continue in future. Because boro is an input intensive crop and requires use of water in the winter season, such a trend would increase pressure on the limited water supply, leading to land degradation, food insecurity.

Other Related Impacts

Other impacts of drought include

• Livelihood activities that rely on sensitive agricultural systems are more vulnerable to climate change events such as drought. 
• Droughts cause major deterioration in household health because their subsequent impact of reducing food consumption leads to substantial increases in illnesses. 
• Fresh water availability in drought-prone areas is also threatened under climate change which affects small-scale fishery activities. 
• Farmers in the drought-prone Barind areas maintain livestock as a risk management strategy to cope with drought impact, even under current climate variability. 
• Incidence of pests and diseases may increase with climate variability and climate change. 

Explore the Drought Monitoring Indices and its Application Procedure

Standardized Precipitation Index (SPI)

The climate of a region is determined by the long-term average, frequency and extremes of several meteorological variables, most notably temperature and precipitation. Precipitation is a precious natural resource and it is quite variable. The index compares very favorably against several other "drought" indices (Keyantash and Dracup, 2002), and has been adopted by the US National Drought Mitigation Center for operational use to replace the traditional Palmer Drought Severity Index (PDSI). 

Some applications of the SPI

Researchers have employed SPI to examine numerous questions such as, drought, teleconnections with large scale circulatory systems, floods and crop yields. El Niño Southern Oscillation (ENSO) phenomenon has been related to several weather and climatic extremes around the world. Fernández and Fernández, (2002) identified several zones in the continental region of southern South America, where teleconnections exist between the extreme phases of ENSO and precipitation zones characterized through the use of SPI. 

Seiler et al. (2002) used SPI to study the recurrent floods affecting the southern Córdoba Province in Argentina, as a tool for monitoring flood risk in that region. They proposed applying SPI as an effective tool for a regional climate risk monitoring system. Sims et al. (2002) compared PDSI and SPI for estimating soil moisture in the western mountains, central piedmont, and the coastal plain in North Carolina, USA. Results suggest SPI to be more representative of short-term precipitation and soil moisture variation and hence a better indicator of soil wetness. Anctil et al. (2002) conducted a regional analysis of 5-day precipitation and demonstrated that SPI can be used beyond its usual diagnostic function, by quantifying the probability that precipitation to come will put an end to an ongoing drought.

Cumulative probabilities of SPI values

In the instance described above, rainfall is the variate in a gamma distribution function. The function will have a standard deviation and a mean which depends on the rainfall characteristics of that area. Standard deviation is often described as the value along a distribution at which the cumulative probability of an event occurring is 0.1587. In a like manner, the cumulative probability of any SPI value can be found, and this will be equal to the cumulative probability of the corresponding rainfall event. In summary therefore, the SPI can effectively represent the amount of rainfall over a given time scale, with the advantage that it provides not only information on the amount of rainfall, but that it also gives an indication of what this amount is in relation to the normal, thus leading to the definition of whether a station is experiencing drought or not. It gives output in units of standard deviation from the average based on as-long-rainfall- dis-tribution-as-there-is-data-for. The longer the period used to calculate the distribution parameters, the more likely you are to get better results (e.g. 50 years better than 20 years). Therefore, you can use a very long time period (e.g. 1920-1998) to calculate the parameters of the distribution and then extract the SPI values for only a given time period (could be one year, or a number of years to give a time series).

Precipitation Data of Rangpur 

The Climate of the District is moderate with equable temperature, high humidity and plenty of rainfall. The summer season commences in April and lasts up to June. The monsoon usually sets in early June and continues till the end of September. The winter season sets in early November and lasts up to the end of February.

Table 3: Precipitation Data.

The northern region of Bangladesh has in recent decades has been afflicted by recurrent and severe droughts, which in turn often led to intense food insecurity, known locallyas Monga. Every year, generally from mid-September through mid-November, this crisis occurs. People call the period Mora Kartik, meaning the month of death and disaster. Too little water in the rivers during the dry seasons and less rainfall creates drought situations. The results indicated that there were significant changes in spatial and temporal conditions of drought in Bangladesh. 

The results of the present study demonstrated that drought is recurrent; and the vulnerability of drought varies spatially and temporarily. On average, drought occurred every 2.5 years in the country. Significant changes were found in the SPI index in three-month, six-month, and twelve-month SPI interfaces. The drought being a changing phenomenon in Bangladesh is mostly unpredictable over the study period. The spatiotemporal character of drought of Bangladesh indicated that the country was vulnerable to drought incidents on the basis of the past rainfall records. The drought varied due to the temporal and spatial pattern of rainfall occurrences. The SPI and PDSI depicted that the drought conditions plunged dramatically in some years whereas in other years they remained stable. Drought hits Bangladesh on an average of 2.5 years which was alarming for agriculture practices and environment issues. Drought was more prominent in northern and south-western regions of Bangladesh compared to the rest of the areas of the country. SPI is only based on rainfall and PDSI is based on rainfall and temperature data. For this, it is easy to detect, monitor, and forecast meteorological drought in a region. The present study helps in understanding drought in different areas in Bangladesh using past rainfall performance. Further, the results may help in planning to take necessary actions to manage regional drought and reduce the adverse impacts of drought across Bangladesh.

The SPI concept was developed to quantify a precipitation deficit for different time scales. While most work has focused on drought conditions, the SPI is equally competent to express magnitudes of excess precipitation, relative to the normal. It was designed as an index that recognizes the importance of time scales in the analysis of water availability and water use. The SPI gives a better representation of abnormal wetness and dryness than Palmer drought indices. The PDSI has been the most prominent index of meteorological drought in the United States, and was intended to retrospectively look at wet and dry conditions using soil water balance techniques. Although the SPI has been in existence for only a decade, it has been used with notable success in various applications, particularly in describing and monitoring drought conditions. It can be used as an indicator of drought severity or excessive wetness, and in the design of drought/flood contingency plans.

In this figure we can see the changing pattern of Drought Scenario in 2000, 2005 and 2010. In 2000 Drought spread the whole Bangladesh. The red marks show Drought intensity. In 2005 Drought mainly spread northern part of Bangladesh. In 2010 drought occurred Bangladesh mainly in northern area.

Palmer Drought Severity Index (PDSI)

Palmer developed this index based on the supply-and-demand concept of the water balance equation. The objective of the index is to measure the departure of the moisture supply for normal condition at a specific location. The PDSI is based on precipitation and temperature data, on the local Available Water Content (AWC) of the soil and other meteorological parameters. The Palmer Index has been widely used but it has some limitations. Among these we mention: the index is highly sensitive to the AWC of a soil type and that there are some difficulties in comparing the results obtained in regions with different water balances. 

The Palmer Index varies between -6.0 and +6.0. The Palmer Drought Severity Index (PDSI) has been used the longest for monitoring drought. The PDSI allows for a categorization of various levels of wetness and dryness that are prominent over an area. The PDSI is calculated based on precipitation and temperature data, as well as the local Available Water Content (AWC) of the soil. Palmer values may lag emerging droughts by several months; are less well suited for mountainous land or areas of frequent climatic extremes; and are complex—has an unspecified, built-in time scale that can be misleading.

Table 4: PDSI Classification.

In December 12-18 days face Drought all over Bangladesh. Other Month can't capture the probability of Drought. The northern region of Bangladesh has in recent decades has been afflicted by recurrent and severe droughts, which in turn often led to intense food insecurity, known locallyas Monga. Every year, generally from mid-September through mid-November, this crisis occurs. People call the period Mora Kartik, meaning the month of death and disaster. Too little water in the rivers during the dry seasons and less rainfall creates drought situations. Statistics show that 92% of water in Bangladesh comes via external rivers and only 8% is local rainfall. According to Bangladesh Meteorological Department, “There was 21 per cent less rain during the monsoon period from June to August in 2009 and the northern districts suffer from drought”. Drought is one of the major environmental stresses in the north that drastically limits the grain yield of rice, a staple food of Bangladeshi people. This causes a lot of people to become unemployed and fall into acute food shortage between late July and early November. During this interim period, there are no alternative agricultural activities left for people and the small non-agricultural sector cannot absorb the seasonally unemployed labour force. Hence, food insecurity in the region is associated with yield reduction in rice and non-availability of wage employment.

Limitation of the Study

The study has limitation; it has a sharp time limitation and lengthy participationary process. Participation itself is a time consuming and lengthy process. In addition, any short of research work need much time to bring out an expected result which can reveal new dimension in the field. Both the process demands many to carry out in a total perspective. As a student it could not be done due to lack of financial support. If anybody wants to do future study on this field the study could be helpful to his or her work. The major limitations of the research are given below:

• Lack of Data: There is a lack of primary and secondary data related to oil tanker collision in Shela River.  
• Time constraint: It was one of the main factors to make the study limited. More time was required to fulfill the wide coverage in the research work. Since it was a complementary study in honours level, maintaining other regular academic activities it was not possible to provide adequate time in this purpose. Moreover, research had to be carried within the academic session due to time limit.
• Other Limitation: A good database is required to carry out any research. Inadequate resources are another factor which hampers the proposal work. 

Bangladesh experiences seven months of arid period from November to May, when rainfall usually becomes low. But severe drought mostly affects the country, particularly north and northwest parts, from March to May (premonsoon) and October to November (post-monsoon). Drought causes price hike, job crisis, drinking and irrigation water crisis, and income loss and food insecurity for rural people. Droughts strike regularly, however it is the limited local capabilities and capacities and the lack of entrance to different forms of assets which make livelihoods of people vulnerable.

Anthropogenic factors and climatic conditions mutually reinforce the chronic livelihoods vulnerability of drought-prone areas in Bangladesh. After completing research wok I suggest some proposal for overcome this situation. These are given below:

• Agricultural practices need to be adjusted with the changing climate and consequently the recurrent floods, droughts and cyclone. 
• Ensurance of community seed bank and food bank by the local communities with the help of agricultural officers and concerned authorities is of utmost importance
• Capacity building of the local communities should be strengthened with the help of the local NGOs in association with governmental and international cooperation. 
• Formal institutional capacities such as local financial institutions and disaster management committees also need to be strengthened.
• Local initiatives need to be taken such as self-help programs and awareness raising campaigns
• Integration of food security and sustainable agriculture with national and international policies considering the changing climate is extremely important
• Physical adaptive measures such as excavation, re-excavation of miniponds,, canals and storage facilities need to be taken for preserving rain water
• Better research activities should be supported such as invention of new drought-tolerant crop, varieties or improved existing crops varieties, and other adaptive and conducive technologies.  
• The budget for agricultural production and investment should be improved and properly distributed among the climate induced impacts affected communities. 
• Sustainably intensification agricultural production by changing the conventional systems for reducing greenhouse gas emissions and other negative environmental is necessary
• There is a need for the adjustment of socioeconomic actions such as market facilitation, livelihood diversification, integration of indigenous knowledge and small-scale cottage industries. 

All praise and complement belongs to Almighty Allah for helping me to accomplish this research study successfully. I would like to express my deep sense of gratitude from the core of my heart to my Thesis supervisor Dr. Md. Nazrul Islam, Professor of the Dept. of Geography and Environment, Jahangirnagar University for his continuous intellectual guidance, scholastic supervision, constructive criticism, editing and constant inspiration throughout the tenure of the research work. I am deeply indebted to my parents for their moral support and sacrifices. I am acknowledging the stuff, Mr. Abdul Hannan Khan, Seminar Librarian of the department of Geography and Environment, Jahangirnagar University. Finally I would like to thanks my obligation to the many people, who were forced to suffer my continued need for assistance, discussion and encouragement at different stages of field work for this research.

The authors declare no conflicts of interest in the present study and also publish it.