Data-driven estimates of evapotranspiration and its controls in the Congo Basin
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Published:2020-08-27
Issue:8
Volume:24
Page:4189-4211
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ISSN:1607-7938
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Container-title:Hydrology and Earth System Sciences
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language:en
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Short-container-title:Hydrol. Earth Syst. Sci.
Author:
Burnett Michael W.ORCID, Quetin Gregory R.ORCID, Konings Alexandra G.ORCID
Abstract
Abstract. Evapotranspiration (ET) from tropical forests serves as a critical moisture
source for regional and global climate cycles. However, the magnitude,
seasonality, and interannual variability of ET in the Congo Basin remain
poorly constrained due to a scarcity of direct observations, despite the
Congo being the second-largest river basin in the world and containing a
vast region of tropical forest. In this study, we applied a water balance
model to an array of remotely sensed and in situ datasets to produce
monthly, basin-wide ET estimates spanning April 2002 to November 2016. Data
sources include water storage changes estimated from the Gravity Recovery
and Climate Experiment (GRACE) satellites, in situ measurements of river
discharge, and precipitation from several remotely sensed and gauge-based
sources. An optimal precipitation dataset was determined as a weighted
average of interpolated data by Nicholson et al. (2018), Climate Hazards
InfraRed Precipitation with Station data version 2 (CHIRPS2) , and the
Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks–Climate Data Record product (PERSIANN-CDR), with the relative weights based on the error magnitudes of each dataset as determined by triple collocation. The resulting water-balance-derived ET (ETwb) features a long-term average that is consistent with previous studies (117.2±3.5 cm yr−1) but displays greater seasonal and interannual variability than seven global ET products. The seasonal cycle of ETwb generally tracks that of precipitation over the basin, with the exception that ETwb is greater in March–April–May (MAM) than in the relatively wetter September–October–November (SON) periods. This pattern appears to be
driven by seasonal variations in the diffuse photosynthetically active radiation (PAR) fraction, net radiation (Rn), and soil water availability. From 2002 to 2016, Rn, PAR, and vapor-pressure deficit (VPD) all increased significantly within the Congo Basin; however, no corresponding trend occurred in ETwb. We hypothesize that the stability of ETwb over the study period despite sunnier and less humid conditions may be due to increasing atmospheric CO2 concentrations that offset the impacts of rising VPD and irradiance on stomatal water use efficiency (WUE).
Funder
National Aeronautics and Space Administration National Oceanic and Atmospheric Administration Stanford Graduate School of Education
Publisher
Copernicus GmbH
Subject
General Earth and Planetary Sciences,General Engineering,General Environmental Science
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