Distribution of small seasonal reservoirs in semi-arid regions and associated evaporative losses

Bassem Mady,Dani Or,Peter Lehmann,Steven M Gorelick

doi:10.1088/2515-7620/ab92af

Bassem Mady, Dani Or + Show 2 more

Open Access

https://doi.org/10.1088/2515-7620/ab92af

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Abstract

To support the increasing demand of a growing population for freshwater, small-sized (<0.1 km2) water reservoirs are necessary in areas with limited infrastructure, especially in water-stressed regions having seasonal and variable precipitation. Seasonal storage in small reservoirs is often overlooked in present inventories. Accordingly, we assessed the current state in semi-arid regions using highly resolved Sentinel-2 satellite imagery. Globally, about 3 million small reservoirs are in operation in semi-arid regions having a total water surface area of 17 800 km2 and seasonal storage of 37 km3, supporting 15% of the world’s population in semi-arid regions. Estimated upper-bound of evaporative losses represent 38% (14 km3) of storage during dry season. The study estimates the evaporation suppression using floating covers and lays foundation to assess the feasibility of this technical solution to increase water savings. Significance and originality statement This study provides new insights into the distribution of seasonal freshwater storage in water stressed regions that support large rural population. We provide the first baseline dataset of this distributed freshwater resource to better assess the sustainability of communities in semi-arid regions with chronic water shortages. Water storage in semi-arid regions is subject to potential evaporative losses of nearly 40% of the stored water. We analyzed conditions where evaporative losses could be significantly reduced using floating covers, a simple and scalable solution suitable for regions with underdeveloped economies. The study as well ranks regions with highest potential benefits from evaporation suppression measures.

Highlights

The long tradition of freshwater storage in reservoirs to meet dry-season needs is likely to expand due to the increasing water demand for food production, in a changing climate of a rapidly growing human population [1]
We provide new global estimates of the spatial distribution and storage capacity of small water reservoirs (0.0003 to 0.1 km2) in semi-arid regions using high-resolution multi-spectral Sentinel-2 imagery
Despite the exponent values’ similarity, we found that the information gap on small reservoirs cannot be extrapolated from existing large dams and lakes data due to the significant difference in spatial densities of small compared to large reservoirs

Summary

Introduction

The long tradition of freshwater storage in reservoirs to meet dry-season needs is likely to expand due to the increasing water demand for food production, in a changing climate of a rapidly growing human population [1]. Small seasonal reservoirs have been used in different regions of the world for centuries, especially in semi-arid regions (known under different local names [2, 3], see figures 1(a)–(e)). In these regions, dry-season water shortages for agricultural livelihood are common and water storage remains a feasible mitigation measure, while more recently, additional off-grid electric power supply was facilitated by means of micro-dams [4, 5]. In contrast with well-studied large reservoirs and dams, small-sized and seasonal freshwater storage systems have relatively low environmental impact [6], yet their distribution and function during dry seasons plays a critical role in promoting the sustainability of rural communities and farmers, and reduce societal inequality gaps [7] for 15% of the world’s population inhabiting semi-arid regions [8]. With development of remote sensing techniques for retrieving salient information from satellite imagery [17–19], the identification of locations, sizes, and usage of small water reservoirs becomes feasible

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