Objective assessment of ecosystem hydrological services in tropical areas: A Colombian experience in arid and semi-arid zones

Abstract This study presents a methodology to address the challenge of objectively demonstrating Ecosystem Hydrological Services (EHS). A case study is used in the region of the La Guajira Peninsula (Colombia), with a focus on the EHS of water flow regulation. The proposed methodology hypothesizes that EHS that have not been objectively demonstrated lead to failures in the implementation of guidelines of Payments for Ecosystem Services (PES). Following this idea, we have tried to understand and quantify the relationship between vegetation coverage and streamflow regulation. To prove this relationship and the existence of the mentioned EHS in the La Guajira Ecosystem, we determined land cover changes from 2000 to 2013 using the Normalized Difference Vegetation Index (NDVI), and we also quantified the streamflow regulation using hydrological and meteorological time series in the study area. The analysis methods used were insufficient to determine the influence of vegetation on hydric regulation EHS; nevertheless, a greater influence of morphometry was observed in medium-and large-sized basins. Another important finding shows the relevance of selecting an adequate spatial and time resolution when quantifying water flow regulation services and its relationship with land cover characteristics. In this way, this exercise shows the complexity of quantifying EHS. Furthermore, we highlight some aspects that must be taken into account to properly quantify streamflow regulation due to vegetation coverage.

摘要 本研究提出了一套可用于客观验证生态系统水文服务（Ecosystem Hydrological Services, EHS）的方法体系，以应对其客观论证过程中的挑战。本研究以哥伦比亚瓜希拉半岛为案例研究区，重点聚焦径流调节类生态系统水文服务。本研究提出的方法体系假设：未得到客观验证的生态系统水文服务，会导致生态系统服务付费（Payments for Ecosystem Services, PES）相关指南的实施失效。基于这一核心假设，本研究旨在厘清并量化植被覆盖度与径流调节功能之间的关联关系。为验证上述关联关系以及瓜希拉半岛生态系统中目标生态系统水文服务的存在性，本研究借助归一化植被指数（Normalized Difference Vegetation Index, NDVI）反演了2000年至2013年的土地覆被变化情况，并通过研究区内的水文与气象时间序列数据量化了径流调节功能。本次研究所采用的分析方法尚不足以明确植被对水文调节类生态系统水文服务的影响效应；不过研究发现，在中大型流域中，流域地貌特征对水文调节的影响更为显著。另一项重要研究结果表明，在量化径流调节服务及其与土地覆被特征的关联关系时，选取合适的空间与时间分辨率至关重要。综上，本次研究实践凸显了生态系统水文服务量化工作的复杂性。此外，本研究还明确了基于植被覆盖度精准量化径流调节服务时需重点考量的若干关键维度。