Introducing a new normalized cryospheric index (NCI) to categorize sub-watersheds on arid environments

Abstract. This study examines sub-watersheds in the arid northern region of Chile (26°41’–28°24’S), situated within the broader Copiapo watershed. The primary water source for this watershed originates from cryospheric reservoirs. The region exhibits pronounced physiographic and climatic diversity, with its northern sector situated within the South American Arid Diagonal (SAAD), where cryospheric features exhibit greater spatial isolation. The aim of this study is to quantify the water volume contributed by distinct cryoforms to regional watersheds. This study employs a classification methodology to categorize cryospheric reservoirs within sub-watersheds, integrating an inventory of cryoforms, historical snow cover data derived from satellite imagery, and published ice content and depth measurements. The Normalized Cryospheric Index (NCI) is calculated under varying hydrological conditions to assess and compare potential water volumes across sub-watersheds. The analysis reveals significant spatial variability in cryospheric reserves and their strategic hydrological significance. Under average and low-precipitation conditions, the southern sub-watersheds of the Copiapo river Basin exhibit the greatest water storage potential. The Montosa river (NCI = 0.82), Manflas river (NCI = 0.62), Estero Come Caballo (NCI = 0.57), and Del Potro river (NCI = 0.51) sub-watersheds have been identified as strategic priority areas within the region for sustaining surface runoff and safeguarding water availability. During high-snowfall periods, northern sub-watersheds in the Copiapo river Basin, such as Estero Come Caballos, exhibit elevated NCI values despite their limited cryospheric reserves. In contrast, the Montosa, Manflas, and Pulido sub-watersheds contain the most extensive cryospheric reserves and rank among the top four sub-watersheds with the highest NCI scores.