Inundation and groundwater dynamics for quantification of evaporative water loss in tropical wetlands

Abstract

Abstract. The remoteness, complexity and heterogeneity of tropical wetlands make the characterisation of their hydrological processes challenging. In particular estimates of evaporative water loss are inherently uncertain. In view of the large influence on the local and regional climate, the quantification of evaporation is essential for the determination of the water balance of permanent and intermittent water bodies. Data for tropical wetlands are scarce where their remoteness impedes direct evaporation measurements. Seasonal inundation dynamics affect evaporation processes in tropical wetlands, which can be analysed in two stages: the first stage during the wet season and the second stage during the dry season. As yet no adequate method exists for determining second stage evaporation without soil moisture data, which are usually unavailable for the remote tropical wetlands. Our study aimed at developing a process-based model to simulate first and second stage evaporation in tropical wetlands. We selected a set of empirical potential evaporation (PET) models of varying complexity, each based on different assumptions and available datasets, and evaluated the models with pan evaporation observations in the Pantanal of South America, one of the largest tropical wetlands in the world. We used high-resolution measurements of surface and groundwater levels at different locations to determine the water available for evaporation. Actual evaporation (AET) was derived by constraining simulated PET based on available water. The model of best fit was applied to different types of water bodies with varying inundation durations and captured first and second stage evaporation. With our new model we could quantify evaporative water loss in the dry and the wet season for different locations in the Pantanal. This new spatially-explicit approach represents an improvement in our understanding of the role of evaporation in the water balance of the Pantanal. We recommend the application of this model in other remote tropical wetlands, since only a minimum of input data is necessary.

Coupled Ground- and Space-Based Assessment of Regional Inundation Dynamics to Assess Impact of Local and Upstream Changes on Evaporation in Tropical Wetlands

“…Based on the seasonal inundation dynamics, we calculated regional evaporation losses with a previously developed approach for the same region. We estimated potential evaporation (PET) and used PET to constrain the estimate of AET based on available water and hence inundation dynamics [16] (Appendix 1). In order to investigate the impact of local and upstream changes on the ecosystem, we also calculated evaporation for the years 2001-2013 and related our results to regional conditions of the study area (precipitation and inflow of tributaries).…”

“…This way, we determined the duration of the dry and wet seasons for the two-year study period. Using this water availability information we calculated daily AET with a recently developed approach (short description provided in Appendix 1), where evaporative water loss was simulated on a local scale [16]. Climatic variables used for this approach were derived from the National Institute of Meteorology in Brazil (INMET-Instituto Nacional de Meteorologia) including air temperature, relative humidity, wind velocity, barometric pressure and cloud cover data from OGIMET (www.ogimet.com).…”

“…Assessing the vulnerability of wetlands to such changes is very difficult, even more where the remoteness results in insufficient ground truthing due to poor or missing gauging stations [10,[12][13][14]. River gauging data do not provide spatial information on the inundation extent in wetlands [15] and evaporation measurements are scarce, which complicates its estimation on a regional scale [16]. Therefore, in the last decades, satellite imagery became an important data source for assessing the status of remote wetland areas.…”

Estoque de energia na biomassa e no ar do dossel de Vochysia divergens Pohl

“…Neste contexto, as dificuldades associadas aos estudos em ecossistemas florestais estão relacionadas à realização das medidas; em sistemas tropicais, por exemplo, há escassez de medições diretas de variáveis, como evaporação (Schwerdtfeger et al, 2014) e, em contrapartida, da estimativa do fechamento do balanço de energia (McCaughey et al, 1997;Barr et al, 2006;Wilson et al, 2002). Uma conclusão geral em referência a isto refere-se ao armazenamento de energia na biomassa que pode constituir um componente significativo do saldo de radiação em ecossistemas florestais durante períodos específicos.…”

Water Balance Analysis over the Niger Inland Delta-Mali: Spatio-Temporal Dynamics of the Flooded Area and Water Losses

“…While most previous studies have underestimated water losses in the basin resulting from evaporation, the main component of water loss in wetlands [17], very few studies have considered additional water losses through water withdrawal for irrigation purposes, that are estimated to amount to 2.69 km 3 /year of water on average [1].…”