Potential of MODIS data to track the variability in ecosystem water-use efficiency of temperate deciduous forests

Abstract

a b s t r a c tOne of the most important linkage that coupled terrestrial carbon and water cycles is ecosystem water use efficiency (WUE), which is also relevant to the appropriate ecosystem management actions. The eddy covariance technique provides continuous observations of carbon and water fluxes at the landscape level, presenting an opportunity to infer ecosystem WUE at daily or annual time scales. Scaling up such measurements to regional or national scale, however, remains challenging. Few studies have been reported on direct estimation of WUE from remotely-sensed data, particularly the seasonal dynamics of forests. Therefore, this study aims to assess the potential of tracking the variability in WUE by exclusively using time-series MODIS data at 8 flux tower sites of temperate deciduous forests. Our analyses showed that the 8-day variations in WUE were mainly subject to control by temperature, solar radiation and vapor pressure deficit. As a proxy of plant response to the environmental controls, MODIS-derived vegetation index was found to strongly correlate with ecosystem WUE and could be used for remote quantification. Then, both performance of the indirect WUE estimated from MODIS GPP and ET products (WUE MOD ) and the direct estimates from MODIS data using the calibrated temperature and greenness (TG) model were evaluated using tower-based measurements (WUE EC ). In general, WUE EC was overly predicted at the start and end of the vegetation period and badly underestimated during the summertime by WUE MOD because of the discrepancy in GPP MOD . However, the proposed TG model provided substantially good estimates of ecosystem WUE in spite of lacking skills in monitoring summer troughs. Independent validation at four additional sites further certified the improvement, which provided a new framework for quantifying the seasonal variations in ecosystem WUE.

Spatiotemporal variations in productivity and water use efficiency across a temperate forest landscape of Northeast China

“…umt.edu/project/modis/mod16.php), which were calculated by using the improved ET algorithm based on the Penman-Monteith (Mu et al 2011). The improved algorithm employed involves simplifying the calculation of vegetation cover fraction, calculating ET as the sum daytime and nighttime components, adding soil heat flux calculation, improving estimates of stomatal conductance, aerodynamic resistance and boundary layer resistance, separating dry canopy surface from the wet, and dividing soil surface into saturated wet and moist surfaces (Mu et al 2011;Tang et al 2016). The ecosystem WUE was calculated from MODIS NPP and ET.…”

Remote Sensing of Ecosystem Water Use Efficiency: A Review of Direct and Indirect Estimation Methods

“…MODIS GPP and ET products are the most widely used and unique high resolution remote sensing data products for the indirect estimation of WUE. Although these products have been used to analyze the temporal and spatial patterns of global WUE for terrestrial ecosystems, the discrepancy with tower-based WUE at 8-day time scales still exist at specific sites [68,75].…”

Remote Sensing of Water Use Efficiency and Terrestrial Drought Recovery across the Contiguous United States

“…However, due to the infeasibility of distinguishing soil and canopy evaporation and plant transpiration from evapotranspiration (ET) [34], either precipitation [35] or ET [36] are used as indicators of water loss (i.e., consumed by the ecosystem). Among various definitions of WUE, the GPP/ET is the most common indicator and it is employed in this study too [1,3,37].…”