Assessment of Anticipated Climate Change Impact on Water Resources in Krishna Basin ASSESSMENT OF ANTICIPATED CLIMATE CHANGE IMPACT ON WATER RESOURCES IN KRISHNA BASIN

The Krishna, one of the longest rivers in southern India with a cultivable area, 77 per cent is experiencing steady changes in atmosphere with erratic rainfall, increased humidity and decreased temperatures. The prime objective is hydrological assessment of future monsoon and its uncertainties for sustainable crop production and irrigation water management practices in a changing climate. The impact of future climate change is assessed using calibrated and validated ArcSWAT modelling tool. The Basin on an average receives 800 mm rainfall in the monsoon period with least of 300mm in the south and a maximum of 2000mm in the west. The basin has surface water potential of 78.1 km3 and groundwater potential of 26.41 km3. The hydrological assessment of the basin based on the IPRC model shows that by mid-century there would be increase in flash floods with prolonged dry spells. The assessment on spatial and temporal distribution of water availability, precipitation, PET and soil water suggests the need for eco-friendly adaptation technologies along with a planned irrigation development to capture in abundance and supply in the deficient period, when the demand is more and a need for efficient crop model to understand and assist the flooding situation.


Introduction
The threat of climate change, population, urbanisation and industrial growth on availability of quality water is slowly lurking into a major global problem of the world. The intensity of spatial and temporal variations of water availability is ever changing with climate change.
The socio-economic growth of the rural community is dependent on crop production and rearing the livestock which is in turn dependent on water availability. Rice is one of the waterintensive crops and more than 75 per cent of the world's rice is produced in irrigated rice lands, which are predominantly found in Asia ( Van der Hoek et al. 2001). Rice grown under traditional practices in the Asian tropics and sub-tropics requires between 700 and 1,500 mm of water for a cropping season depending on soil texture (Bhuiyan 1992). Water demand will grow from 656km3 in 2010 to 1069 km3 by 2050 (Thatte et al. 2009). Hence, India has to gear up to the changing climatic conditions to maintain the production rates to feed the increasing population both at the State, national and global levels.
Researchers are looking at the adaptations strategies that could help the farmers to improve the production and income in the context of changing climate and increasing water scarcity.
As rice is a high water demanding crop, its production will be riskier in future due to

Methodology
The Krishna basin is a water stressed basin, approaching a closing state, where discharge into the ocean has decreased rapidly from 1960 to 2005 due to irrigation expansion (Biggs et al. 2007 Development,Vol.37,No. (2), April-June:2018 chemical yields and nutrient balances in complex basin Srinivasan et al., 1998).
The major advantage of the model is that, unlike other conventional conceptual simulation models, it does not require much calibration. The model can be used for the assessment of existing and anticipated water uses and water shortages (Gosain et al., 2005).

Input Datasets
The source of the digital elevation model Planning (Reddy et al.,1996), Nagpur, India. The soil map has the attributes such as soil texture, depth, drain, nutrient, soils, AWC (Available water capacity), Landform and Erosion. A copy of Andhra Pradesh Soils-Profile Characteristics by Water Technology Centre (ANGRAU), was used to collect the soil characteristics wherever it was needed. Detailed soil data at 1:2,50,000 were prepared only for a portion of the Delta region.

Bias Adjustment of Precipitation Data
Simulations made by any Regional Hence, bias adjustment of rainfall data is a prerequisite for hydrologic modelling.

Hydrologic Modelling
SWAT was used in this study to assess the effect of climate change on the water resources.

SWAT Model Setup for Estimating Water Demand
For assessing the water demand, it is very important that accurate information on the spatial extent of paddy cultivation, the season during which it is grown at a particular place and the length of the growing season, the cropping sequence/rotation and the irrigation source (surface or groundwater) are input in the model.
For this, district-wise agricultural information on principal crops grown, cropping patterns, cropping sequence, sowing period, harvest   (Brouwer et al, 1989). As the crop growth could also be affected due to nutrient stress (lack of nutrients), which will have a cascading effect on the crop ET and irrigation water demand, the auto fertiliser option was triggered, so that the crops growth will not be impaired due to nutrients.

Hydrological Response To Climate Change:
The spatial and temporal distribution of hydrological response to climate change in terms of potential evapotranspiration, soil water content and water yield is estimated and analysed for baseline scenario (current condition), Y1B scenario in mid-century and A1B scenario in endcentury.

Spatial Distribution of Average Annual Water Yield
Baseline 1981  The spatial and temporal distribution of water availability at some of the major reservoirs is studied for baseline, Y1B scenario mid-century and A1B scenario end-century. The water availability was assessed in terms of average flow hydrographs and flow duration curves.

Water Demand
The potential irrigation water demand for paddy was simulated in SWAT by assuming that unlimited supply of water is available to meet the crop consumptive use requirements. The assumption made in this simulation run is that the extent of irrigated area remains the same in current and future climate. This simulation showed that the crop irrigation water demand is expected to reduce in the future. This reduction is due to increased rainfall and reduced potential evapotranspiration.
Potential evapotranspiration is affected not only by the temperature but also by the CO2 concentration. It is known that increase in CO2 would increase plant productivity and decrease the stomatal conductance of the leaves for transpiration. The level of CO2 maintained in the model was 350ppm for baseline, 550ppm for Y1B (mid-century) and 650ppm for A1B (end-century), respectively. Although the temperature increase due to global warming would increase the soil evaporation, the increase in CO2 reduced the transpiration, thus effectively reducing the potential evapotranspiration and hence the irrigation water requirement in the future climate.

Conclusion
In this study, the effect of climate change on the water resources of Krishna river basin was assessed. Hydrographs and flow duration curves at the important discharge stations and reservoir locations were analysed. This information is quite useful for the irrigation engineers to make a decision of when to expect the water and when to release it and how much of it could be stored.
The climate change simulations show that there would be a considerable increase in total Due to reduced PET and increased rainfall, the future irrigation water demand is also expected to be lesser than the current level.