Development of water accounts for the selected sub basins of Brahmaputra, Barak and Irrawady-Chindwin basins in the state of Nagaland using water accounting plus (WA+) framework (PDS-31)

Abstract

Increasing competition for land and water resources is expected in the future due to rising demands for food and bioenergy production, biodiversity conservation, and changing production conditions due to climate change. Growing competition for water in many sectors reduces its availability for irrigation. Thus, efficient approaches are required for effective management of water in every sector particularly in agriculture. With advanced technological development like satellite-based Remote Sensing and Geographical Information System, tools are becoming useful to account the water resources of a region. Water Accounting Plus (WA+) is a python-based tool designed to provide explicit spatial information on water depletion and the net withdrawal process of a region using globally available open access data. In regions such as Nagaland with data unavailability or scarcity, use of freely available open access data is quite handy in accounting the water resources. The major objective of this study is to apply the newly developed WA+ framework for the selected sub-basins of Brahmaputra, Barak and Irrawady-Chindwin (Tizu) basins in the state of Nagaland for estimating the status of the water resources. Few major findings from the study are: From the CHIRPS rainfall data analysis for the period 2001-02 to 2019-20, it was found that a considerable amount of rainfall is falling in the northern and north-eastern parts of Nagaland draining into the Brahmaputra basin. Sub-basins falling in the Brahmaputra basin generates maximum yield for the state of Nagaland. The water accounting-based land use (WALU) suggested that forest cover dominates in the state followed by shrub land, fallow land, agriculture, and built-up area. The area of four land use management classes viz. protected land use (PLU), utilized land use (ULU), Modified land use (MLU) and managed water use (MWU), were 134.42 Km2, 12425.58 Km2, 3651.25 Km2 and 373.10 Km2 respectively. WA+ tool was set-up for the period 2001-02 to 2019-20. Six factsheets viz. Sheet 2 (evapotranspiration), Sheet 3 (part 1: agricultural water consumption; part 2: land and water productivity), Sheet 4 (part 1: man-made utilization; part 2: natural utilization), Sheet 5 (surface water), Sheet 6 (groundwater) and Sheet 1 (Resource base) were generated. Sheet 2 revealed that an average water loss of 14.91 BCM (~ 900 mm) is occurring in the form of evapotranspiration from different basins and sub-basins annually. 37% of the ET loss is beneficially contributing to the intended purpose. The remaining loss of 63% is non-beneficial, and can be suitably converted to beneficial component by adopting suitable agronomical and mechanical measures. Sheet 3 estimated a total agricultural water consumption of 2.50 BCM and 2.55 BCM, predominantly met from the rainfall, during a dry and wet year respectively. Overall, the average land productivity was found to vary from 2564.2 to 4028.3 kg/ha/year and 6149.6 to 7818.9 kg/ha/year during the period 2001-02 to 2019-20, respectively for rainfed and irrigated cereals. The WP was found to vary from 0.66 to 1.02 kg/m3 (with an overall average of 0.83 kg/m3) and 1.90 to 2.56 kg/m3 (with an overall average of 2.2 kg/m3) for rainfed and irrigated cereals respectively. Spatial maps of land and water productivity provide the areas performing well (progressive farmers with high productivity) and poor (farmers with low productivity) in a large basin. These rich information enables the water managers to understand the interventions undertaken at local level by both progressive and less progressive farmers. This helps in planning different interventions for a particular area for higher productivity. The annual average gross withdrawal for man-made and natural land uses are 0.8 BCM and 1.94 BCM respectively. It can be seen that water utilized for natural purposes is almost double than the man-made utilization. Out of the total man-made utilizations, almost 63% of withdrawal was from the surface water. Whereas, surface water utilization was 23% for the natural land uses. The total outflow from the seven sub-basins viz. Dhansiri, Chathe-Dzuza, Doyang, Dikhu, Tizit, Tsurang and Milak to the river Brahmaputra were about 14051 MCM. The estimated outflow from the catchment within the Nagaland to the Barak and Tizu (Irrawady Chindwin) basins were about 572 MCM and 4435 MCM respectively (Sheet 5). As per the estimates in Sheet 6, an annual vertical recharge of 15.68 BCM was estimated, out of which 87% was contributing to the baseflow. Groundwater withdrawal was about 1.77 BCM. An average annual gross inflow of 29 BCM of water was estimated in the study. A net inflow of 28.5 BCM was estimated with a net storage contribution of -0.5 BCM (a negative sign indicates net recharge). The committed flow, as provisioned in the WA+ framework, was estimated to the tune of 3.1 BCM. An annual average of 15.3 BCM of water is available for utilizations in the state, of which about 22% (3.4 BCM) is utilized, and the remaining 11.7 BCM of water was available for utilization (utilizable flow), but yet to be harnessed. Out of the total net inflow into the basin (28.5 BCM), 48% of water is consumed to meet mainly the ET requirements (ET green and ET blue). The study estimated an annual average outflow of 16.2 BCM (Sheet 1). Although all the estimates from WA+ was not validated, but the rich information available from the study provides a preliminary accounting of the water resources for the state of Nagaland entirely based on the satellite-based open access datasets. This will help the planners, policy makers and others associated in the water sector for undertaking appropriate actionable measures.