Recent Seasonal Variations in Ecosystem Water Use Efficiency in China's Key Tropical‐Subtropical Transitional Zones in Response to Climate Change

Abstract

Understanding the response of terrestrial ecosystem water use efficiency (WUE) to climate change is critical to accurately represent the carbon‐water cycle processes. However, how WUE dynamics are evolving under seasonal climate variations and biome‐specific characteristics remains still unclear. In this study, we integrated two state‐of‐the‐art retrieval algorithms to estimate gross primary productivity (GPP) and evapotranspiration (ET) from satellite MODIS records. Such metrics served as input to quantify ecosystem WUE, expressed as the ratio of GPP to ET, and explore its dynamics during the dry and wet season from 2001 to 2018 in China's key tropical to subtropical transitional zones, that is, Yunnan Province. Results show large spatial and seasonal variability in WUE over the observational period. During the dry season, the increasing trends in GPP and ET have led to contrasting WUE patterns in forest and non‐forest biomes, leading to positive and negative WUE trends, respectively. During the wet season, the declining trends in GPP occurring in combination with opposite trends in ET, have caused decreasing WUE consistently across all biomes except croplands, likely further modulated by human factors. The observed changes in WUE appear primarily driven by variations in air temperature (Ta) and vapor pressure deficit (VPD) during both dry and wet seasons. Overall, these results contribute to a better understanding of the carbon‐water interplay in tropical‐subtropical transitional zones and provide new insights to improve our capacity to predict the terrestrial ecosystem's response to climate change.

Impact assessment of agricultural droughts on water use efficiency in different climatic regions of Punjab Province Pakistan using MODIS time series imagery

“…MODIS‐based NDVI 16‐day products (MOD13Q1) with a spatial resolution of 250 m. While GPP 8 days (MOD17A2) available with a spatial resolution of 500 m, and ET of 8 days (MOD16A2) with a spatial resolution of 500 m was taken from (https://www.earthdata.nasa.gov/) as shown in Table 1. ET and GPP were developed using the Penman‐Moneith equation and light use efficiency model (Liu et al, 2022). All these datasets were downloaded using the MODIS library and packages in R software version R i386 4.0.3 from 2001 to 2022 (https://cran.r-project.org/bin/windows/base/) (Baig et al, 2020).…”

“…WUE is the ratio of biomass by plants or crops to the amount of water consumed. WUE also refers to measuring the interchange between water loss and the increase of carbon in terrestrial ecosystems, as shown in equation (Liu et al, 2022; Qin et al, 2023). $$$$ WUE=\frac{GPP}{ET}.$$…”

Evaluation of Ecosystem Water Use Efficiency Based on Coupled and Uncoupled Remote Sensing Products for Maize and Soybean

“…The coupled product can effectively avoid internal inconsistencies between ET and GPP from the uncoupled product and therefore could provide higher-accuracy eWUE estimates [13]. Over the years, a large amount of eWUE-related research (e.g., the spatial and temporal variation of eWUE, the response of eWUE to drought and natural and human activities, and the driver of eWUE changes [1,[39][40][41][42][43][44][45][46][47][48]) has been conducted for various PFTs (including but not limited to cropland); however, most of these studies calculated eWUE based on the MODIS product, whose accuracy is strongly queried by this study as well as previous studies [2,13,49]. This study indicates that the coupled product is more suitable and effective to be applied in the eWUE-related research for different crop species to reduce the uncertainty from the inaccurate RS-based eWUE estimates from the uncoupled products.…”

“…Ecosystem water use efficiency (eWUE), the ratio of gross primary production (GPP, the total amount of carbon fixation by vegetation through photosynthesis) and evapotran-spiration (ET, the sum of evaporation from soil and transpiration through plant leaves), is a critical indicator connecting the terrestrial carbon and water cycles and reflecting multiple ecosystem functions [1,2]. Cultivated cropland accounts for approximately 12% of the Earth's non-ice-covered land surface and provides indispensable survival supplements (e.g., food and fiber) for human beings [3,4].…”