Changes in moisture and energy fluxes due to ground-water based irrigation in the Indian Monsoon Belt

The Indian monsoon belt is home to a large part of the world’s population and agriculture is the major land-use activity in the region. In this poster we present a conceptual synthesis of the impact that agricultural activity can have on the atmosphere and regional climate through irrigation and its feedback on the atmospheric moisture flux and water cycles. The analysis builds on estimating the potential impact that irrigation and related agricultural activities have for modifying the atmospheric conditions within the Indian monsoon belt. These modified atmospheric conditions could potentially lead to changes in the interannual variability in the monsoon rainfall, and perhaps more directly to changes in the intensity of inland rain events. We found that vapor fluxes have increased by 17% (340 km3) with a 7% increase (117 km3) in the wet season and a 55% increase (223 km3) in the dry season. Two-thirds of this increase is attributed to irrigation; at least half of irrigation water is withdrawn from groundwater stores which may be introducing additional water to the hydrologic cycle. The area-averaged change in latent heat flux across India was estimated to be 9 Wm-2. The largest increases in vapor and latent heat fluxes occurred where both cropland and irrigated lands were the predominant contemporary land cover classes (particularly northwest and north-central India). The largest decreases in vapor and energy fluxes occurred where the original moist tropical forests were replaced by agriculture (particularly southern India). The impacts of these changes and other societal factors affecting the water resource vulnerability and economic, societal and water feedbacks are also highlighted. Introduction Human modifications to the hydrologic cycle are in few places felt as acutely and urgently as in India. India leads the world in total irrigated land and irrigation withdrawals represent 92% of all water use. Furthermore, more than 50% of total irrigated area is dependent on groundwater in India (CWC, 2000) and approximately 60% of irrigated food production depends on irrigation from groundwater (Shah et al., 2000). Between 1950 and 1985, surface water withdrawals for irrigation doubled, while groundwater withdrawals increased 113-fold (Sampat, 2000), resulting in rapidly declining groundwater levels in as many as 15 states (Bansil, 2004). An important question is whether such alteration of the hydrologic cycle simply results in a collection of localized impacts or do these alterations produce feedbacks that are significant at regional scales. There is increasing evidence that the latter is true. For example, Figure 1 illustrates potential changes in weather patterns due the conversion of a natural landscape to irrigated cropland in the midwestern U.S. Traditionally, the effects of changes in atmospheric composition (i.e., increased CO2 concentrations) on land processes have been investigated with regional to global general circulation models, a so-called “top down” approach that does not always sufficiently simulate the linkages and non-linear responses of land-atmosphere interactions (Niyogi et al. 2002). Pielke and de Guenni (2004) proposed a new vulnerability paradigm that is place-based, has a “bottom-up” perspective, and focuses on the resource of interest (in our case, freshwater). Figure 2 (adapted from Pielke, 2004) illustrates the impacts of water resource vulnerability on human and natural systems in India.