Abstract
The Tehuacán-Cuicatlán Biosphere Reserve, Mexico (TCBR) is the southernmost arid or semi-arid zone with the highest biodiversity in North America and is a UNESCO World Heritage site. Two main hydrographic streams cross the TCBR, the Salado River (an endogenous river) and the Grande River (an exogenous river). This study investigated temperature anomalies over the past 40 years. We analyzed potential differences between sub-basins and riparian areas on both streams using various indices, namely the Global Warming Index (GWI), Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), and Normalized Difference Drought Index (NDDI), and analyzed the potential relationship of these indices with climate change. Time series of satellite-based precipitation (June 2000–December 2020) and air temperature (January 1980–December 2020) were analyzed. A set of Landsat 8 OLI TIRS imagery from the driest and wettest months (2013–2020) was used to estimate NDVI, NDWI, and NDDI. These indices were evaluated separately for the sub-basins and river corridors in the dry and rainy seasons. The precipitation records indicate that in the Grande river sub-basin, precipitation is higher than in the Salado river sub basin. Normalized temperature anomalies and the GWI suggest a warming trend from 1994 to 2020, increasing up to 0.86°C in the Salado River and 0.52°C in the Grande River. The Grande and Salado sub basins showed significant differences between dry and wet seasons for each index (NDVI, NDWI, and NDDI). A Discriminant Analysis showed that the Salado sub-basin and the Salado River corridor are associated with severe drying conditions in the dry season (highest NDDI values). In the wet season, the Grande River corridor showed intermediate values of NDVI and NDWI but low values of NDDI. The Grande River corridor in the dry season was characterized by intermediate values of NDVI, NDWI, and NDDI. These river corridors provide environmental services in a trade-off with the stream and should be considered biodiversity hotspots. Due to the accentuated warming trend and the lowest precipitation, the Salado River sub-basin showed desertification signs associated with climate change. Both the Salado and the Grande River corridors showed resilience strategies to face climatic conditions.
Highlights
Drylands are a concept that applies to the vast hyper-arid, arid, semi-arid, and dry-sub-humid environments of the Earth, covering about 40–50 percent of the Earth’s land surface (Tooth, 2000; Safriel and Zafar, 2005)
Rivers can be classified as exogenous or exogenic systems when they originate outside the arid zone, while endogenous rivers originate within the dryland zone
This study explores differences in the riverbanks of the Salado and Grande rivers, to investigate the role of intermittent or perennial flows on the maintenance and health status of the respective river corridors through several remote sensing methods and geographic information systems (GIS), including the application of normalized difference indices such as Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), and Normalized Difference Drought Index (NDDI)
Summary
Drylands are a concept that applies to the vast hyper-arid, arid, semi-arid, and dry-sub-humid environments of the Earth, covering about 40–50 percent of the Earth’s land surface (Tooth, 2000; Safriel and Zafar, 2005) These are defined as regions where the annual potential evapotranspiration greatly exceeds annual precipitation, showing an aridity index lower than 0.65 (Tooth, 2013; FAO, 2016; Huang et al, 2017). Endogenous rivers generally have an intermittent flow, with channels remaining typically dry and only occasionally transporting water and sediments (Tooth, 2000); they can be perennial in some cases Both types of rivers run across drylands, providing different attributes and environmental services to dryland sub-basins. River corridors may differ between exogenous and endogenous rivers
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