Spatio-temporal variation of temperature characteristics over Narmada basin - is the consistent warming trend a possible climate change signal?
The analysis of the high resolution gridded data (1° x 1°) of daily maximum, minimum and mean temperature for the 23 grids covering the Narmada basin has detected varying trends in the upper, middle and lower zones of the basin, based on the 40 years data from 1961-2008. The annual 1-day maximum temperature has been steadily increasing at the rate of 1.10°C/100 yr, but the annual 1-day minimum temperature depicted a much higher rate in increase of 3.20°C/100 yr with significant rising trend at 95% significance level (test statistic: Z = +1.989) based on the non-parametric Mann-Kendall test for detection of trend in time series. The zone-wise temperature variation has been studied for two distinct time periods, each of 20 years viz. 1969-88 and 1989-08. A divergent pattern is observed in minimum daily temperature trends in the various zones of the basin with significant rising trends in the lower zone and no significant trend in the upper zone during both time periods. Also a significant rising trend has been detected in the diurnal temperature range (DTR) in the lower zone during August (Z = +2.21), with no significant trends in other months. Significant rising trends have been detected in the mean monthly temperatures in the upper and middle zones, with no significant trend in lower zone. Similar pattern of significant rising trend have been detected in mean monthly temperatures during the principal winter (December and January) and summer months (April and May) in upper and middle zones of the basin. However, no significant trend has been detected during the principal monsoon months (July and August) for all the zones. As the basin is located in a semi-arid region and the perennial flows result from the contribution from the soil moisture and groundwater storages, any increase in the maximum and minimum temperatures will change the water availability scenario due to increased water demands from higher consumptive use requirements. To study the water demand scenario in the various zones in the basin, the potential evapotranspiration (PET) has been computed. Significant rising trends in PET were detected in all the zones, during the 1989-08 time slot, which indicates higher crop water requirement from the agriculture sector due to the increased temperatures. The comparison of the zonal annual rainfall (AR) with the actual evapotranspiration (AET) which gives an indication of the supply-demand scenario, has found that the annual AET has been greater than AR in the middle zone on 5 occasions during 1969-88 and subsequently increased to 10 occasions during 1989-08, whereas in the lower zone the AET was greater than AR during most of the years in both time periods. This indicates increased water demands and lower rainwater availability under the changing climate scenario, in the middle and lower zones of Narmada basin, which calls for effective water resources development and management strategies.
Analysis of monsoon rainfall variability over Narmada basin in central India: Implication of climate change
Daily rainfall of 23 high resolution (1° x 1°) grid cells covering the Narmada basin has been analyzed to investigate the trend in extreme rainfall events. The trend analysis of the 1-day maximum rainfall series showed a significant positive trend at 95% significance level with the Mann-Kendall test statistic value of z = 3.66 over the entire basin. The analysis further suggested that there has been an increasing trend in the magnitude of 1-day maximum rainfall over the basin with more areas in the basin experiencing high intensity storms, which was more prominent in the most recent 20 years. Drought duration estimated by the standardized precipitation index for the periods 1951-1970 and 1989-2008 indicated that the entire basin has experienced frequent droughts during the recent two decades, with the middle zone of the basin being more prone to droughts. The analysis also suggested that appropriate measures may be proposed for better management of the water resources in the basin, and also for mitigation of floods and droughts, considering the increased risk of the high intensity storms as well as the increased frequency of drought occurrence during the recent two decades.
Impact of water conservation structures on the agricultural productivity in the context of climate change
The temporal variability of rainfall in rainfed regions is one of the main factors for their low agricultural productivity. The future climate projections show an increased variability of rainfall, thus further impacting the rainfed agriculture. The change in rainfall pattern is expected to alter the cropping period and making the crop sowing date critical to mitigate crop failure. However, with enhanced temporal variability of rainfall, arriving at an optimal crop sowing date is a challenging task. One of the widely adopted measure to improve the agricultural productivity in the rainfed regions is water harvesting structures (WHS). This study evaluates the ability of the WHS in absorbing the shock of the temporal variability of the rainfall on the agricultural productivity. In addition, the efficacy of the structures in improving the agricultural productivity in the future climate projections is also evaluated. The proposed analysis is performed over Kondepi watershed in Andhra Pradesh, India, where water conservation measures are implemented by Government and Non-Government Organizations. The results of the study show that the WHS can minimize the sensitivity of the agricultural productivity to the crop sowing date. The extended availability of water in WHS resulted in removing the relationship between crop sowing date and crop productivity, thus exhibiting the ability of WHS in dams in absorbing the shock caused by the temporal variability of the rainfall. Further, the agricultural productivity was found to be increasing due to the presence of WHS in both current and future climate conditions.
Dynamic integration of land use changes in a hydrologic assessment of a rapidly developing Indian catchment
Rapid land use and land-cover changes strongly affect water resources. Particularly in regions that experience seasonal water scarcity, land use scenario assessments provide a valuable basis for the evaluation of possible future water shortages. The objective of this study is to dynamically integrate land use model projections with a hydrologic model to analyze potential future impacts of land use change on the water resources of a rapidly developing catchment upstream of Pune, India. For the first time projections from the urban growth and land use change model SLEUTH are employed as a dynamic input to the hydrologic model SWAT. By this means, impacts of land use changes on the water balance components are assessed for the near future (2009-2028) employing four different climate conditions (baseline, IPCC A1B, dry, wet). The land use change modeling results in an increase of urban area by + 23.1% at the fringes of Pune and by + 12.2% in the upper catchment, whereas agricultural land (- 14.0% and - 0.3%, respectively) and semi-natural area (- 9.1% and - 11.9%, respectively) decrease between 2009 and 2028. Under baseline climate conditions, these land use changes induce seasonal changes in the water balance components. Water yield particularly increases at the onset of monsoon (up to + 11.0 mm per month) due to increased impervious area, whereas evapotranspiration decreases in the dry season (up to - 15.1 mm per month) as a result of the loss of irrigated agricultural area. As the projections are made for the near future (2009-2028) land use change impacts are similar under IPCC A1B climate conditions. Only if more extreme dry years occur, an exacerbation of the land use change impacts can be expected. Particularly in rapidly changing environments an implementation of both dynamic land use change and climate change seems favorable to assess seasonal and gradual changes in the water balance.
Optimal reservoir operation – A climate change adaptation strategy for Narmada basin in central India
The potential impacts of climate change on the water resources of the Narmada basin in central India has been investigated using the Soil and Water Assessment Tool (SWAT). The existing dams in the river basin have been incorporated in the model setups, calibration and validation. The COordinated Regional climate Downscaling EXperiment datasets for South-Asia (CORDEX-SA) at 0.5° × 0.5° resolution for four-time horizons, viz., 1970–05 (historical), 2006–40 (near-term), 2041–70 (mid-term) and 2071–99 (end-term) under Representative Concentration Pathways (RCP) scenarios, RCP4.5 and RCP8.5 has been used to investigate the changes in the future climate and simulation of future streamflow. The proposed dams have also been incorporated for modeling the future developmental scenarios. The scenario analysis based on the projected climate variables has led to the inference that the change in the precipitation pattern coupled with the warming trends, maybe contributing towards higher variability in water availability. A future scenario of lower water availability and higher water demands thus calls for optimal utilization of available water resources in the future, so that the higher water demands can be satisfied with lower anticipated future flows. Various alternatives were explored for devising adaptation strategies using the engineering/technical solutions in which the optimal water resources management approaches were explored using the simulation-only and the genetic algorithm based simulation–optimization approaches. The simulation–optimization framework based integrated reservoir operation of four reservoirs has led to better reservoir performance and the number of irrigation failures has decreased substantially from 92 to 12 during 2006–40, 86 to 22 during 2041–70 and 89 to 10 during 2071–99. The hydropower failures have also decreased considerably from 202 to 96 during 2006–40, 192 to 28 during 2041–70 and 179 to 67 during 2071–99 under the RCP8.5 scenario. There were no failures in meeting the domestic water supply and environment flow demands. This may be an important adaptation measure to address the issues of climate change impacts on the water resources in the future in the Narmada basin.