Dynamic Monitoring of Surface Water Area during 1989–2019 in the Hetao Plain Using Landsat Data in Google Earth Engine

TLDR

Spatio‑temporal changes in surface water are critical for agriculture, economy, society, and ecosystem function in the Hetao Plain. The study aimed to map long‑term surface water area in the Hetao Plain from 1989 to 2019 using all available Landsat images and the mNDWI, EVI, and NDVI indices within Google Earth Engine. Surface water was mapped from 7534 Landsat scenes with mNDWI, EVI, and NDVI, and precipitation, temperature, and irrigated area were analyzed to assess climate and human impacts on long‑term changes. Across 31 years, the Hetao Plain’s maximum, seasonal, and annual average water body area declined while the number of water bodies rose; area changes were mainly driven by maximum water bodies, number changes by minimum water bodies; precipitation positively influenced both area and number, whereas temperature and irrigation had negative effects, informing water resource management.

Abstract

The spatio-temporal change of the surface water is very important to agricultural, economic, and social development in the Hetao Plain, as well as the structure and function of the ecosystem. To understand the long-term changes of the surface water area in the Hetao Plain, we used all available Landsat images (7534 scenes) and adopted the modified Normalized Difference Water Index (mNDWI), Enhanced Vegetation Index (EVI), and Normalized Difference Vegetation Index (NDVI) to map the open-surface water from 1989 to 2019 in the Google Earth Engine (GEE) cloud platform. We further analyzed precipitation, temperature, and irrigated area, revealing the impact of climate change and human activities on long-term surface water changes. The results show the following. (1) In the last 31 years, the maximum, seasonal, and annual average water body area values in the Hetao Plain have exhibited a downward trend. Meanwhile, the number of maximum, seasonal, and permanent water bodies displayed a significant upward trend. (2) The variation of the surface water area in the Hetao Plain is mainly affected by the maximum water body area, while the variation of the water body number is mainly affected by the number of minimum water bodies. (3) Precipitation has statistically significant positive effects on the water body area and water body number, which has statistically significant negative effects with temperature and irrigation. The findings of this study can be used to help the policy-makers and farmers understand changing water resources and its driving mechanism and provide a reference for water resources management, agricultural irrigation, and ecological protection.