Yvan Caballero

Projected impacts of climate change on farmers' extraction of groundwater from crystalline aquifers in South India

Local groundwater levels in South India are falling alarmingly. In the semi-arid crystalline Deccan plateau area, agricultural production relies on groundwater resources. Downscaled Global Climate Model (GCM) data are used to force a spatially distributed agro-hydrological model in order to evaluate Climate Change (CC) effects on local groundwater extraction (GWE). The slight increase of precipitation may alleviate current groundwater depletion on average, despite the increased evaporation due to warming. Nevertheless, projected climatic extremes create worse GWE shortages than for present climate. Local conditions may lead to opposing impacts on GWE, from increases to decreases (+/−20 mm/year), for a given spatially homogeneous CC forcing. Areas vulnerable to CC in terms of irrigation apportionment are thus identified. Our results emphasize the importance of accounting for local characteristics (water harvesting systems and maximal aquifer capacity versus GWE) in developing measures to cope with CC impacts in the South Indian region.

A methodology for regionalizing 3-D effective porosity at watershed scale in crystalline aquifers

13 An innovative approach for regionalizing the 3-D effective-porosity field is presented and 14 applied to two large, overexploited and deeply weathered crystalline aquifers located in 15 southern India. The method derives from earlier work on regionalizing a 2-D effective-16 porosity field in that part of an aquifer where the water table fluctuates, which is now 17 extended over the entire aquifer using a 3-D approach. A method based on geological and 18 geophysical surveys has also been developed for mapping the weathering profile layers 19 (saprolite and fractured layers). The method for regionalizing 3-D effective porosity 20 combines: water-table fluctuation and groundwater budget techniques at various cell sizes 21 with the use of satellite based data (for groundwater abstraction), the structure of the 22 weathering profile and geostatistical techniques. The approach is presented in detail for the 23 Kudaliar watershed (983 km 2), and tested on the 730 km 2 Anantapur watershed. At watershed 24 scale, the effective porosity of the aquifer ranges from 0.5% to 2% in Kudaliar and between 25 0.3% and 1% in Anantapur, which agrees with earlier works. Results show that: i) depending 26 on the geology and on the structure of the weathering profile, the vertical distribution of 27 effective porosity can be very different, and that the fractured layers in crystalline aquifers are 28 not necessarily characterized by a rapid decrease in effective porosity; and ii) that the lateral 29 variations in effective porosity can be larger than the vertical ones. These variations suggest 30 that within a same weathering profile the density of open fractures and/or degree of 31 weathering in the fractured zone may significantly varies from a place to another. 32 The proposed method provides information on the spatial distribution of effective porosity 33 which is of prime interest in terms of flux and contaminant transport in crystalline aquifers. 34 Implications for mapping groundwater storage and scarcity are also discussed, which should 35 help in improving groundwater resource management strategies. 36 37

ESPERE—A Multiple‐Method Microsoft Excel Application for Estimating Aquifer Recharge

Several methods can be used to estimate groundwater recharge. These vary in terms of time scale and the nature of the data they treat. ESPERE, an MS Excel application, uses several different commonly-used methods to rapidly and simultaneously estimate recharge. It makes it possible to quantify recharge with a monthly and annual time step and to visualize related uncertainties. It was designed to limit the number and type of parameters that must be entered by the user so that it could be used in any context, including those in which knowledge is limited. It provides an excellent means of analyzing the behavior of an aquifer in response to recharge.

ESPERE, a multiple-method Microsoft Excel application for estimating aquifer

Several methods can be used to estimate groundwater recharge. These vary in terms of time scale and the nature of the data they treat. ESPERE, an MS Excel application, uses several different commonly-used methods to rapidly and simultaneously estimate recharge. It makes it possible to quantify recharge with a monthly and annual time step and to visualize related uncertainties. It was designed to limit the number and type of parameters that must be entered by the user so that it could be used in any context, including those in which knowledge is limited. It provides an excellent means of analyzing the behavior of an aquifer in response to recharge.