Evapotranspiration estimates for two tropical mountain forest using high spatial resolution satellite data

ABSTRACT

Tropical Mountain Forest (TMF) provides important ecological functions like evapotranspiration (ET) that supplies moisture and energy to the atmosphere. ET observations are scarce and difficult to accomplish particularly in areas of high heterogeneity where TMF are. Remote sensing (RS) allows to quantify and to determine ET spatial variation at the landscape level. Detail imaginary improves high spatial variability retrieval. Thought the greater detail introduces cast shadows by trees which hamper image interpretation. The objective of this study is to characterize ET estimation for the TMF of the southern Ecuadorian Andes by combining meteorological data with high-resolution satellite images. Shadows from high resolution images were masked out by applying focal statistics. The analysis included two meteorological periods typical of the area; a wet period when rain prevails and a dry period when precipitation is more sporadic. The reference evapotranspiration (ET₀) was calculated using the FAO-Penman Montheid method by applying data obtained from an automatic weather station. The enhanced vegetation index (EVI) was derived from 2 m resolution WorldView2 satellite images. Results showed a lower ET mean value during the wet period: 1.54 mm day⁻¹ compared to 2.37 mm day⁻¹. Two forest types, differentiated from its structural composition and topographical position (ravine and ridge), marked ET spatial variation. Ravine forest that has a more dense and closed canopy showed higher ET values for both meteorological conditions. A comparison between ET estimations and ET field measurements from a scintillometer device showed a good agreement (coefficient of correlation $r$ = 0.89) that proves the validity of the method. This study demonstrates that the application of high spatial resolution improves ET estimation in TMF especially when shadows are removed. Also, emphasizes the importance of analysing spatial heterogeneity to properly assess ecosystem water flux terms.

Disclosure statement

The authors declare no conflict of interest.

Data Availability

The Meteorological data (radiation, temperature, relative humidity, and wind speed) used to support the findings of this study have been deposited in: Environmental changes in biodiversity hot spot ecosystems of South Ecuador: RESPonse and feedback effECTs. Dataset ID: 497. Dataset creators: Rütger Rollenbeck and ThorstenPeter. Contact: Thorsten Peters and Rütger Rollenbeck. http://vhrz669.hrz.uni-marburg.de/tmf_respect/#

The Satellite images – WorldView2 (16 June 2012 T15:52:47/05 November 2013 T16:10:35) used to support the findings of this study were supplied by GAF under license and so cannot be made freely available.

The Scintillometer data to support the findings of this study have not been made available because final results are not published. Data will be public available on line, in the repository of:Environmental changes in biodiversity hotspot ecosystems of South Ecuador: RESPonse and feedback effECTs (FOR2730) http://vhrz669.hrz.uni-marburg.de/tmf_respect/#

Additional information

Funding

This work was financially supported by the Deutsche Forschungsgemeinschaft [grant number BE 1780/38-1]. P. Álava Núñez gratefully acknowledges funding from the Katholischer Akademischer Ausländer-Dienst (KAAD). We thank the Ministerio del Ambiente of Ecuador for research permission No. 021-2013-DPL-MA and No. 010-IC-FAU/FLO-DPZCH -MAAll. The authors also want to thank the anonymous reviewers for their valuable comments;Katholischer Akademischer Ausländer-Dienst [Scholarship];