Remotely Sensed Land Surface Temperature-Based Water Stress Index for Wetland Habitats

Abstract

Despite covering only 2–6% of land, wetland ecosystems play an important role at the local and global scale. They provide various ecosystem services (carbon dioxide sequestration, pollution removal, water retention, climate regulation, etc.) as long as they are in good condition. By definition, wetlands are rich in water ecosystems. However, ongoing climate change with an ambiguous balance of rain in a temperate climate zone leads to drought conditions. Such periods interfere with the natural processes occurring on wetlands and restrain the normal functioning of wetland ecosystems. Persisting unfavorable water conditions lead to irreversible changes in wetland habitats. Hence, the monitoring of habitat changes caused by an insufficient amount of water (plant water stress) is necessary. Unfortunately, due to the specific conditions of wetlands, monitoring them by both traditional and remote sensing techniques is challenging, and research on wetland water stress has been insufficient. This paper describes the adaptation of the thermal water stress index, also known as the crop water stress index (CWSI), for wetlands. This index is calculated based on land surface temperature and meteorological parameters (temperature and vapor pressure deficit—VPD). In this study, an unmanned aerial system (UAS) was used to measure land surface temperature. Performance of the CWSI was confirmed by the high correlation with field measurements of a fraction of absorbed photosynthetically active radiation (R = −0.70) and soil moisture (R = −0.62). Comparison of the crop water stress index with meteorological drought indices showed that the first phase of drought (meteorological drought) cannot be detected with this index. This study confirms the potential of using the CWSI as a water stress indicator in wetland ecosystems.

Thermal and Optical Indices for Wetland Habitats, are They Showing the Same Thing?

“…In the empirical approach these values are calculated based on measured linear relation (called non-water-stressed baseline -NWSB) of dT and vapour pressure deficit (VPD). The NWSB for this type of plant community was determined by [52] as fallow: = −11.63 • + 21.32…”

“…Previous study on using CWSI in the wetlands at the local scale (using UAV data) shows that it can be used for this type of ecosystem as water stress indicator [52]. Hence, as the first step correlation of tower based (ground truth) CWSI and Landsat-8 TIRS based CWSI were analyzed.…”

“…It is caused by conditions required for robust CWSI calculation. Data for the CWSI calculation should be acquired in clear sky conditions, during low wind speed and after a few hours of direct sunlight [52], hence aggregation tower CWSI for longer period is biased by changing meteorological condition. Results from the satellite dataset (Section III.…”

“…Summarizing satellite based CWSI for the wetland habitat based on used NWSB [52] is applicable at big (catchment) scale. Nevertheless, it should be performed with proper data quality assessment to make sure that meteorological and remotely sensed give robust CWSI results.…”

The Gavkhouni Wetland Dryness and Its Impact on Air Temperature Variability in the Eastern Part of the Zayandeh-Rud River Basin, Iran

“…Wetlands, as aquatic ecosystems, provide a variety of benefits to wildlife and humans in many different ways [1,2]. Some of the services provided by wetlands include reducing greenhouse gasses, regulating climate [3], purifying water, storing pollutants in their soils, and vegetation maintaining water supply [4], providing breeding habitat for various species of fauna, and flora, and biodiversity function [5]. Wetlands are one of the vital micro-components of climate as they have their own specific moisture cycles with aquatic plants [6].…”