Faculty Publications

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Regional climate trends and topographic influence over the Western Ghat catchments of India
(John Wiley and Sons Ltd vgorayska@wiley.com Southern Gate Chichester, West Sussex PO19 8SQ, 2018) Mudbhatkal, A.; Mahesha, M.
This study investigates the role of elevation stratification and climate change on the hydrology of Western Ghat catchments during the period from 1951 to 2013 using gridded data. The trend analysis of rainfall and temperature was conducted using the Mann–Kendall trend test, and the hydrological modelling of the rivers was conducted using the Soil and Water Assessment Tool (SWAT) model. To characterize the spatial distribution of rainfall and streamflow based on elevation stratification, contemporary rainfall zones were delineated and the response of each zone was evaluated. The results indicated that the maximum rainfall occurs at certain distance on the windward side from the crest of the Western Ghats. On the leeward side (eastern plateau), the rainfall is maximum at crest (Western Ghats) and decreases with distance. The rivers in the southern portion of the Western Ghats of India were highly vulnerable to changing climate followed by the central portion. The annual and monsoon rainfall in the southern river decreased at 0.43 and 0.30% decade?1 (1% significance level), respectively. The summer rainfall in the river of the central portion (Netravathi River) decreased at 0.44% decade?1. The annual air temperature of the southern river catchment (Vamanapuram) increased at the rate of 0.12 °C decade?1 (at 0.1% significance level), and the air temperature of the central rivers increased at the rate of 0.09, 0.08, and 0.07 °C (0.1% significance level), respectively. The streamflow response of the southern and central rivers was discernible as the monsoon flow decreased at 37% decade?1 (0.1% significance level) in the southern river and 10% decade?1 (5% significance level) in the central river. Interestingly, the pristine Aghanashini River demonstrated resilience to climate change with an increase in annual rainfall and streamflow at 115 mm decade?1 (5% significance level) and 0.71 Mm3 decade?1 (0.1% significance level), respectively. © 2017 Royal Meteorological Society
Multivariate analysis of concurrent droughts and their effects on Kharif crops—A copula-based approach
(John Wiley and Sons Ltd, 2022) Muthuvel, D.; Mahesha, M.
Apart from creating an ecological imbalance, drought events could affect an agrarian country's economy and food security by reducing crop yields. The antecedent meteorological droughts could prolong into hydrological and (or) agricultural droughts and may co-exist as concurrent droughts. The current study aims to comprehensively study Indian concurrent droughts, their effects on crop yield, and possible teleconnection with ENSO (El Niño–Southern Oscillation), adopting a copula-based multivariate approach. The copula functions can replicate the correlation among the variables and keep the dependence structure intact. The concurrent drought characteristics are computed using a multivariate standardized drought index that incorporates the three primary drought indices using the Gaussian copula. Some of the severe concurrent drought years such as 2002, 1987, 1972, and 1965 caused considerable yield losses in Kharif season crops of groundnut, millet, and rice. This prompts to construct quad-variate models involving the crop yield and the three drought indices using the vine copulas that perform better than the elliptical and symmetric Archimedean copula. Though the isolated forms of droughts could cause mild yield losses, the probability of concurrent droughts causing high to exceptional losses is more. Further, the ENSO teleconnection with the concurrent monsoon droughts is analysed and mapped. The above-normal warming of the Nino 3.4 region over the tropical Pacific during the months leading up to the monsoon could signal concurrent monsoon droughts in the areas under the Ganga-Brahmaputra basin at a probability of around 45%. These results could be helpful in drought mitigation measures and policymaking. © 2021 Royal Meteorological Society.
Regional Trends and Spatiotemporal Analysis of Rainfall and Groundwater in the West Coast Basins of India
(American Society of Civil Engineers (ASCE), 2022) Krishnan, C.; Mahesha, M.
The present study investigates the spatiotemporal variabilities of long-term (1950-2016) rainfall and regional groundwater levels for annual and seasonal periods over the west coast of India. The study area is a narrow strip of land between Western Ghats (mountainous terrain) and the Arabian Sea, extending over 1,500 km from south to north. The Mann Kendall (MK) and Sen's slope estimator established the long-term trend and magnitude of rainfall and groundwater. The nature of trends in the time series of hydroclimatic variables was identified through singular spectrum analysis (SSA). The SSA extracted nonlinear trends along with the shape for both increasing and decreasing trends. Annual and southwest monsoon rainfall exhibited prominent decreasing trends. The percentage departure analysis of rainfall revealed that earlier decades (1950-1980) were the wettest, followed by the drier decades (1980-2016) for Periyar, Varrar, and Netravati and vice versa for Vasishti and Bhatsol. The wavelet spectra for rainfall indicated short- and long-term modulations. The long-term groundwater level trends of 725 wells on the entire west coast showed a significant decline in 13% of wells, and 6% of wells indicated increasing trends. The Monte Carlo-based numerical investigations on the modified MK (mMK) test power indicated the influence of parent distributions on trend detection. The field significance of trends at a 5% significance level was examined using the bootstrap test. The precipitation data were then compared with groundwater level variation at each site, and correlations were established. The declining southwest monsoon rains and their uneven spatial distribution could be attributed to a subsequent decline in the region's postmonsoon groundwater levels. © 2022 American Society of Civil Engineers.

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