Exploring the Effect of Rainfall Variability and Water Extent in Tanguar

Tanguar haor is located in the north-eastern region of Bangladesh and frequently experienced extreme events such as high rainfall that affect the haor basin area with flash floods on a regular basis. Tanguar haor is usually foreseen to severe disastrous conditions for the reason of changes in rainfall patterns and water extent. The study was conducted at Tanguar haor of Sunamganj district. This study mainly focuses on the year to year rainfall variability (2001-2018) and water extent (2002-2018) in the Tanguar haor area. The specific objective of the study was to explore the effect of rainfall variability and water extent in Tanguar haor. Information and data were collected mainly from secondary sources. Analysis of data and assess the ecological effect of changes in rainfall patterns and water extent were the main activities of the study along with others. The findings of the study were changeability in rainfall patterns and water extent frequently caused a flash flood in pre-monsoon and monsoon season in the Tanguar haor area. Flash flood causes a vast amount of financial loss for the living people of the Tanguar haor that makes them more vulnerable to live well. The result of this study may help to gather new knowledge on the consequences of rainfall variability and water extent in the haor basin area. It may add the significance for the management of flash flood and severe stress in haor basin area.

Bangladesh with an area of 147,570 sq. km that lies between 20°34'-26°38' N, and 88°01'-92°41' E (Rashid, 1991). Bangladesh is widely recognized as one of the most climate vulnerable countries in the world. Haor basin area situated in north-eastern part usually characterizes with large to medium flood plain depressions (Sara et al., 2013). Hydroecological features of haor basin area are flood plain and marshy lands covered approximately 1.99 million hectares of area and accommodating approximately 19.37 million of people (BHWDB, 2012). Haor areas are generally featured as bowlshaped large tectonic depressions and receive large amount of surface runoff water by rivers, khals and become very extensive water body in the monsoon but dries up mostly in the post-monsoon period (Bevanger et al., 2001;and IUCN, 2002). Now-adays Bangladesh predicted as most vulnerable country due to climate change (rainfall and water extent) particularly in haor basin area on account of geographic location, feature of flood plains, growing density of population, extreme poverty and very high dependency on the natural resources (Rahaman et al., 2014). Covering 9,727 hectares, Tanguar haor in north-east part of Bangladesh, adjacent to the Indian border, is part of wetland of the Surma-Kushiyara rivers basins (BHWDB, 2012).
Nowadays the variability of climatic parameter has become a challenging issue. Tanguar haor (ecosystem, livelihoods, and living people) are especially sensitive to the different natural disasters including flash flood, drought and storm surges (Munasinghe, 2000). Rainfall as well as temperature is two major climatic variables that structured the socioecological system (Klain, 1998). Any change in rainfall pattern and temperature cycle and water extent as a result of climate change caused flash flood in Tanguar haor (Elahi, 1988). Climatic feature of Tanguar haor are subtropical monsoon nature with three dominating seasons likely summer, monsoon and winter. Summer is from April to June and temperature ranges from 30.9 to 33.4 degree celsius. Winter is from October to February and temperature ranges from 8.5 to 16.6 degree celsius (Rahaman et al., 2014). Average annual rainfall is 8000 mm in northern part of Sunamganj. Within Sylhet region out of total annual rainfall 65-69% rainfall occurs in summer. The spring experiences with 21-23% of annual rainfall and the autumn experiences with 6-8% of annual rainfall (Rahaman et al., 2014). High rainfall during pre-monsoon season causes flash flood in haor area (Munasinghe, 2000).
Tanguar haor in Sunamganj district of Sylhet division experiences high variability in rainfall and water extent on a regular basis. This causes flash flood event more severe in the Tanguar haor. During low water level the haor area experiences drought condition but very less in average. Due to climate change, high population density, environmental degradation causes several natural disasters in haor area. But flash flood event are more frequent in this area rather than others. There has been relatively little scientific research characterizing the variability in rainfall and water extent as outcomes of flood hazards and similarly, little social science research targeting how vulnerable populations perceive to flood risks through mitigation strategies. Rainfall is one the major determinants of flood severity in Bangladesh especially in the haor basin area. Recent floods have turned into catastrophe due to huge water flow from the upstream point and regional rainfall acted as an auxiliary factor which accelerates the situation to be worst. During the month of November to February the Tanguar haor area experiences low rainfall and water extent, March to May experiences medium or average rainfall and water extent and in the month of April to September the experiences high rainfall variability and water extent. Due to heavy rainfall the study area usually experiences flood in monsoon season but, sometimes during pre-monsoon season heavy rainfall and streams from mountains area raises the water level of bounded rivers that flows to the haor basins and causes flash flood in the Tanguar haor of Sunamganj. Northern parts and the eastern parts of Bangladesh usually affects by the extent of flash floods. A flash flood is considered with the high rises of water level of rivers and subsequent overbank discharge with very high velocity due to high rainfall. In Tanguar hoar area, flash flood arises after math of heavy rainfall, rises of water level in the Surma River and heavy inundation in the adjacent hills and mountains. These floods often destroy the standing crops at the ripening stage and cause severe damages to the physical infrastructures along haor basin area (Saju et al., 2020).
Considering all of these issues this study focuses on the variability in rainfall pattern and water extent in Tanguar haor area. The specific objectives of the study were as follows: (i) to analyze major climate change parameters (rainfall, water level); (ii) to find out the effect of rainfall variability and water extent in the study area; (iii) to follow up some measures for the management of flash flood in Tanguar haor area. This study may help to reveal the actual scenario and to take practical actions for the management of flash flood and ecological balance in the haor basin area.

MATERIALS AND METHODS:
Selection of the Study Area -The study was conducted at Dharmapasha and Tahirpur upazilas of Sunamganj District in Bangladesh. Sunamganj is situated in the Sylhet division with the Sylhet district adjacent to east, Habiganj district in south and Netrokona district in west (Siddiqi, 2012). The Surma, Kushiyara and Danuka river go through the district where as the Ratna River crossed the Sunamganj district. Sunamganj has a maximum of 33.2 degree celsius and a minimum 13.6 degree celsius annual average temperature with annual rainfall of 3334 mm (Ashfaq, 2012). There are many haor and beel (wetlands ecosystems) in Sunamganj. Tanguar haor in Sunamganj district has particular wetland ecosystem of countrywide importance and already came into international focus with the international recognition as Ramsar sites and world heritage by UNESCO. Geographical position of Tanguar haor is at 25°06' to 25°11' N and 91°01' to 91°06' E. The area of Tanguar haor includes 46 villages within the haor basin is approximately 100 km 2 of which 2,802.36 ha 2 is wetland (Asfhaq, 2012). It is the source of livelihood for more than 40,000 people (IUCN, 2007).
Study Design -Every stage for the formulation of this study was very important. Some of the methodological steps of this study are as follows: (i) Literature review has been done; (ii) Data of rainfall (2001-2018) and water level (2002-2018) has been collected; (iii) An appropriate analysis has been done on the basis of collected information and data from secondary sources that may help to assess the rainfall variability and water extent in the study area; (iv) Monthly average rainfall (mm) data records of Sylhet division, Sunamganj district and Tahirpur Upazila of Tanguar haor has been analyzed form year 2001 to 2018; (v) Annual water level anomaly (mm) data of Sunamganj district has been analyzed and Monthly average water level (m) data records of Surma river at Tanguar haor has been analyzed from year 2002 to 2018; (vi) Analysis of rainfall variability and water extent has been done to find out its effect on ecological settings of the study area and (vii) Finally some strategies have been follow up for the management of flash flood in Tanguar haor basin area that will help to take both proactive and reactive activities to minimize the effects of flash flood.
This study is mainly based on secondary sources of data and information. The secondary sources of data were as follows: Climate Change Knowledge Portal, International Union for Conservation of Nature (IUCN) project and from different report, research articles, books, journal papers and many more related to it.

Rainfall Variabilityand Water Level in Tanguar Haor
Climate change parameter (rainfall, water level) data in Tanguar haor -From Climate Change Knowledge Portal and IUCN, the collected data on rainfall (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018), and water level (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018) for this study are as follows and shown in Table 1.   Monthly average rainfall records of Sunamganj (2001-2018) -Because of its location in the tropical monsoon region, the quantity of rainfall is very high in Sunamganj. In the early portion of the premonsoon season, a contracted zone of air mass incoherence lies over the country that sometimes flows from the southwestern part to the northeastern part (IUCN, 2014). When season headways, this discontinuity deteriorates and departures toward northwest and with draws with the end of the season whilst makes spaces for the beginning of the summer monsoon. Rainy season that overlaps with the summer monsoon is branded by southerly or southwesterly winds with very high humidity, high rainfall and extended repeated days of rainfall that     . Due to increased rainfall and streams in Sunamganj district, the mean sea level or water level of Surma river increased and that's why this district specially haor area experiences flash flood events (Muzaffar and Ahmed, 2006). During dry season due to rainfall shortage and decrease of mean sea level of Surma river the district experiences drought situation and portable water crisis but it is less in average. Annual average sea 10    This study found that the pattern and quality of water flowing through the wetlands have been altered substantially due to changing flow pattern in feeder river such as Surma river as well as various water management and infrastructure development schemes in Tanguar haor areas. During the wet seasons, water levels within the haor area gradually rise as water flows from the Surma rivers into the haor. In dry season, water level recedes as reversal of flow takes place with the falling stage in rivers as well as evaporation exceeds rainfall. It is observed that July-September period represents high flow season and November-April period low flow season. Due to heavy rainfall the study area usually experiences flood in monsoon season but, sometimes during pre-monsoon season heavy rainfall and streams from mountains area raises the water level of study area bounded rivers that flows to the haor basins and causes flash flood in the Tanguar haor of Sunamganj. Tanguar    This study found the highest variability in rainfall and water extent during the pre-monsoon season when flash flood normally occurs. The effect of rainfall variability and water extent in Tanguar haor causes the flash flood more frequently than other climatic events.

Chronological events of flash flood and its effects
Flooding in Bangladesh is a normal and frequently recurrent phenomenon. Flash flood is the most common types of floods in Bangladesh. Flash flood arises from the overflow of the bank of hilly rivers, rain causes floods due to poor drainage systems, sometimes monsoon floods in the flood plains of major adjacent rivers and coastal floods occurs from following storm surge due to variability in rainfall pattern and due to very high water extent. Haor basin area of Bangladesh affected mostly by the events of flash flood than the other region because of low lying land covered in the haor basin area. Chronological events of flood and its effects are shown in Table 2.  Table 3.    Table 3 shows that Sunamganj district has been affected most extensively due to flash flood in 2017. According to Department of Agricultural Extension (DAE), 2017 total area affected (under boro cultivation) in Dharmapasha and Tahirpur upazila was 50,200 hec and damage of standing crops in boro field was 26,220 hec. Main problem associated with the Tanguar haor was heavy rainfall and extent water logging that causes frequent flash flood. Effect of flash flood in Tanguar haor is shown in Table 4. Tanguar   In low water season the floral composition going to dries up that causes the diversity of floral composition. Faunal compositions of Tanguar haor are fish species, amphibians, reptiles, birds and mammals (BLI, 2012). High water level in the Tanguar haor sometimes causes the increases of faunal composition. Living places of faunal composition are changes that cause the migration of faunal species.

Extent Water Level and its Influences in Ecological Settings in
Water influences on agricultural crop production -Agricultural crop production is the main livelihood activities of the people of Tanguar haor area. Boro crop are mainly cultivated here. During monsoon season high water level causes the crop production damaged. All of the cultivated land goes under the water and crops are destroyed. During pre-monsoon season sudden flash flood destroy the crops of the haor area. In post monsoon season means the drought season causes the water scarcity but it is less in amount, it causes the crop production hampered.
Water Influences on fisheries -The fisheries resources of Tanguar Haor is very amusing and has a high importance in terms of fish production, fish habitat, breeding support, national economy and livelihood support. The haor is very important in terms of fish species diversity. Most common fish species found in Tanguar  Long term steps -Some long-term suggestions that may be found useful in strengthening protection practices during flash floods are as follows: (i) earthen embankment is an economically smart intervention for protecting flash flood events. However, limitations such as difficulties of physical works and weak management set-up for operation, maintenance and protection, including lack of engagement of community people in the process needs to be addressed effectively for involving all key actors; (ii) effect minimizing strategies such as the practices of cropping patterns, which minimizes the exposure to losses and setting up of nonagricultural income-generating activities need to be promoted. Crop type and pattern should be selected according to susceptibility of flood. Effort should be taken by concerned agencies to find out new variety of crops resilient in combating flash floods; (iii) any livelihood initiative in the haor areas need to take into consideration the flood history so that the initiative does not give in, rather yield some amount of benefit to the targeted and affected people. Involvement of the community and enlisting their inputs in the any kind of program design and relevant issues affecting their livelihood will make the intervention process more effective, easier and impact bearing; (iv) mainstreaming disaster risk reduction and climate change adaptation in the existing development works and future initiatives of different government departments and Non-Governmental Organization (NGOs) working in the areas need to redesign their development program with active participation of the most vulnerable communities to ensure that they maximize flood mitigation potential and incorporate traditional community cropping practices which can fit technically, environmentally and economically and socially; (v) well organized and coordinated effort is needed to strengthen local level planning, decision making process and allocation of resources to local government bodies; (vi) measures for forecasting flash floods should be geared up. Improvement of present forecasting system is very much needed. Flash flood related awareness raising activities need to be provided. Cross boarder steps should be explored by technical authorities in this regard; (vii) coping adaptation strategies such as migration, reconstruct houses, job switching, and changes in crop calendar, follow weather forecast and early warning system are more important for the management of flash flood in haor basin.

CONCLUSION:
Tanguar haor experiences high rainfall variability and water extent during pre-monsoon period when flash flood normally occurs. Any rotation of rainfall and water extent as a result of climate change causes flash flood in the Tanguar haor basin area. During the wet seasons, water levels within the haor area gradually rise as water flows from the rivers into the haor. The rivers in the Tanguar haor basin are flashy in nature and flash floods occur in the pre-monsoon months of March to May. This study has done an appropriate analysis of rainfall and water level of Tanguar haor based on information and data collected from secondary sources. This study founds high rainfall variability and flash flood as more frequent climatic events in this haor region. The outcome of the study may help to incorporate new concept about the ground level significance of flash flood management in haor basin area. Results from this study action may take care of all responsible authority to increase the practices of coping adaptation strategies due to high rainfall variability and water extent. It is certainly can act as a substitute to detailed and in-depth analysis at the level of concern.