Sedimentary records from human-made talavs reveal climate risks in semi-arid watersheds of India

Abstract

Assessing climate impacts in semi-arid watersheds, which are home to populous semi-arid regions of South Asia, is becoming increasingly critical as these regions emerge as climate hotspots. Century-scale records of climate impacts, preserved in terrestrial sedimentary archives, are some of the only kinds of investigations that can provide the necessary insights into how local climate variations impact these watersheds. Here, we investigate sedimentary records preserved in unique types of human-made water bodies, which are commonly present in arid and semi-arid regions of south Asia. Known as ‘talavs’, human-made water bodies are ubiquitous in south Asia and have been historically constructed by damming seasonal rain-fed distributaries in order to conserve rainwater for the purposes of sustenance and agriculture in water-stressed regions. Integrating a multidisciplinary approach comprising remote sensing, lake geophysics, lithostratigraphic (sedimentological, mineralogical & geochemical measurements) and radiometric dating, we reconstruct century-scale records of landscape erosion & resultant run-off and in water-stressed catchments in one of the most climatologically threatened watersheds of western India, namely the Bhima watershed. Our reconstructions show that land erosion and subsequent sediment deposition in talavs are tied to the regional expressions of the Indian summer monsoon (ISM). We also find that while run-off is sensitive to divisional expressions of hydroclimate variability (associated with the ISM), the intensity of run-off and resultant erosion is not a simple function of rainfall intensity; in fact, we find that land-surface erodibility is impacted by land-use patterns and incidence of prior climate events (e.g. flooding) and that these compunded effects are more prominent in drier catchments (which also experience more extreme climate events) than in the wetter parts of the watersheds. Based on our investigation, we conclude that drier catchments of watersheds in semi-arid regions are at an elevated risk of direct climate impacts compared to the wetter catchments in the same watershed.