Modeling water regulation ecosystem services: A review in the context of ecosystem accounting

Natural Capital Accounting (NCA) has evolved rapidly in recent years through substantial efforts of both international organizations and the scientific community. Water regulation ecosystem services (ES) are key elements of regulating services in ecosystem accounting, with most relevant studies strongly relying on models for ES quantification up to now. In this paper, we provide a review of modeling efforts for water regulation ES based on 148 scientific papers, properly systematized, analyzed and interpreted by using a detailed and structured original template. We examined emerging trends and gaps in model applications and the readiness to integrate them into the NCA and SEEA-EA frameworks. We propose a classification scheme which organizes the 92 different models and modeling approaches identified in the review process into eight model categories so that this scheme can be efficiently used in the water ES assessment of and for further integration into the accounting framework. Among the models, the hydrologic model SWAT and the modeling tool InVEST are by far the most popular. The results of the review revealed differences between the general ES literature and the accounting-related papers. Moreover, our analysis sets the basis for useful recommendations of which model categories are the most appropriate for the water regulation ES, included in the SEEA-EA reference list. Based on the number of relevant papers, the reliability and the confidence level of the recommendations for the use of models have been incorporated in our analysis. We highlight as model category with the highest confidence the ones relative to quantification water flow and flood control service aiming at ES accounting. Models for erosion control ES can only be recommended with a lower confidence, while for water purification the results lack clear evidence for using a particular group of models. Based on the research findings we identified the main research priorities on model integration in the accounting of water regulation ES: 1) further development of guidelines for the use of models in ecosystem accounting; 2) analyses of the spatial aspects of the model towards a clear distinction between ecosystem service supply and use; and 3) development of integrated modeling approaches for water regulation ES accounting.