Why is the Arkavathy River drying? A multiple-hypothesis approach in a data-scarce region

Abstract

Abstract. Water planning decisions are only as good as our ability to explain historical trends and make reasonable predictions of future water availability. But predicting water availability can be a challenge in rapidly growing regions, where human modifications of land and waterscapes are changing the hydrologic system. Yet, many regions of the world lack the long-term hydrologic monitoring records needed to understand past changes and predict future trends.We investigated this "predictions under change" problem in the data-scarce Thippagondanahalli (TG Halli) catchment of the Arkavathy sub-basin in southern India. Inflows into TG Halli reservoir have declined sharply since the 1970s. The causes of the drying are poorly understood, resulting in misdirected or counter-productive management responses.Five plausible hypotheses that could explain the decline were tested using data from field surveys and secondary sources: (1) changes in rainfall amount, seasonality and intensity; (2) increases in temperature; (3) groundwater extraction; (4) expansion of eucalyptus plantations; and (5) fragmentation of the river channel. Our results suggest that groundwater pumping, expansion of eucalyptus plantations and, to a lesser extent, channel fragmentation are much more likely to have caused the decline in surface flows in the TG Halli catchment than changing climate.The multiple-hypothesis approach presents a systematic way to quantify the relative contributions of proximate anthropogenic and climate drivers to hydrological change. The approach not only makes a meaningful contribution to the policy debate but also helps prioritize and design future research. The approach is a first step to conducting use-inspired socio-hydrologic research in a watershed.

The Groundwater Recovery Paradox in South India

“…Geophysical Research Letters, 46, 9602-9611. https:// doi.org/10.1029/2019GL083525 Experiment (GRACE) satellites, water level measurements in groundwater monitoring wells, and global hydrological models. The problem is that these findings contradict on-the-ground field reports and farm surveys that report increasing well failures during the same time period (Merriott, 2015;Srinivasan et al, 2015).…”

Prediction in a socio-hydrological world

“…A range of tools, such as role play, serious gaming (Voinov et al 2016) and decision theatres (White et al 2010), exist that can be adopted in socio-hydrological modelling to elicit values, beliefs and norms, understand actor responses to different environmental states and also educate them about the biophysical implications of their actions. However, building useful models does not necessarily have to involve formal stakeholder interactions; reference to contemporary debates can also be used to identify salient questions and thus the scope of the model (Srinivasan et al 2015, Garcia et al 2016. If the goal is to explore outcomes that are useful, sociohydrological modellers must be willing to go out on a limb and seek unconventional data at the scale and granularity needed.…”

Drying Urban lakes: A consequence of climate change, urbanization or other anthropogenic causes? An insight from northern India

“…In Bangladesh, Islam, Kitazawa, Runfola, and Giner (2012) suggested the filling up of the bed, causing lake degradation in Dhaka. Srinivasan et al (2015) discussed the drying up of TG Halli Reservoir and cascading reservoirs near Bangalore in South India. Srinivasan et al (2015) stressed urban exploitation as the predominant reason, resulting in a declining groundwater table.…”