Land Use Policy Scenarios Research Articles

A coupled modeling approach to assess the effect of forest policies in water provision: A biophysical evaluation of a drought-prone rural catchment in south-central Chile

The effect of different forest conservation policies on water provision has been poorly investigated due to a lack of an integrative methodological framework that enables its quantification. We developed a method for assessing the effects of forest conservation policies on water provision for rural inhabitants, based on a land-use model coupled with an eco-hydrological model. We used as a case study the Lumaco catchment, Chile, a territory dominated by native forests (NF) and non-native tree farms, with an extended dry period where nearly 12,600 people of rural communities get drinking water through water trucks. We analyzed three land-use policy scenarios: i) a baseline scenario based on historical land-cover maps; ii) a NF Recovery and Protection (NFRP) scenario, based on an earlier implementation of the first NF Recovery and Forestry Development bill; and iii) a Pristine (PR) scenario, based on potential vegetation belts; the latter two based on Dyna CLUE, and simulated between 1990 and 2015. Impacts on water provision from each scenario were computed with SWAT. The NFRP scenario resulted in an increase of 6974 ha of NF regarding the baseline situation, and the PR scenario showed an increase of 26,939 ha of NF. Despite large differences in NF areas, slight increases in inflows (Q) were found between the NFRP and the PR scenarios, with relative differences with respect to the baseline of 0.3% and 2.5% for NFRP and PR, respectively. Notwithstanding, these small differences in the NFRP scenario, they become larger if we analyze the cumulative values during the dry season only (December, January, and February), where they reach 1.1% in a normal year and 3.1% in a dry year. Flows increases were transformed into water truck costs resulting in up to 441,876 USD (monthly) of fiscal spending that could be avoided during a dry period.

Modeling the effect of urbanization on flood risk in Ayamama Watershed, Istanbul, Turkey, using the MIKE 21 FM model

Urbanization is one of the most important factors that affect flood risk. Flood risk is, thus, expected to increase in the future with further urbanization in various parts of the world. In order to overcome flood risk, appropriate measures need to be taken based on a deep understanding of the risk levels under various urban extents as such studies are essential to formulate effective measures. In this study, the dynamic cellular automata-based urbanization model called SLEUTH was used to model urbanization in Ayamama Watershed, a watershed located in Istanbul, Turkey, under three landuse policy scenarios: current trend, east–west-oriented growth trend and growth trend under Project Canal Istanbul (PCIT). The outputs of the urbanization modeling, together with hydrographs of various return periods determined using the Peak-Over-Threshold value method and other required inputs, were used to investigate the effects of urbanization on flood risk using the hydrodynamic two-dimensional flexible mesh model, known as MIKE 21 FM. The results of the study showed that allowing unrestricted urbanization (dense development under PCIT scenario) in Ayamama Watershed will lead to considerable increase in the size of land inundated by flood when compared to the other scenarios. Thus, not allowing further development in the watershed is the best alternative. However, if the implementation of the PCIT scenario is inevitable, limiting the level of development in such a way that it does not result in considerable change in the flood risk is recommended. In addition, improving the drainage system in the watershed could further reduce the flooding risk.

Assessing the Hydrological Response of Ayamama Watershed from Urbanization Predicted under Various Landuse Policy Scenarios

This study investigated the effects of urbanization predicted using the SLEUTH urban growth model (an acronym taken from Slope, Landuse, Exclusion, Urban extent, Transportation and Hillshade) under four landuse policy scenarios on the hydrological response of Ayamama watershed using the Hydrologic Engineering Center Release 1 (HEC-1) hydrological model. The SLEUTH model was calibrated based on the Brute Force Monte Carlo iteration technique using the urban extents of Istanbul in 1987, 2000, 2009 and 2013 and was verified by considering Kappa coefficient as evaluation criteria. HEC-1 was calibrated and verified using observed rainfall-runoff event and based on the coefficient of determination (R2), Nash-Sutcliffe coefficient of efficiency (CE) and percentage of bias (PBIAS) as performance indicators. The urbanization prediction results showed that the urban extent of Ayamama watershed would reach 50.3 km2, 44 km2, 63 km2 and 60 km2 under Scenarios 1, 2, 3 and 4, respectively, in 2050. The hydrological simulation results under these urban extents showed that the urban extent of Ayamama watershed under Scenario-3, a scenario that allows unrestricted growth with the implementation of Project Canal Istanbul (PCI), resulted in the highest peak discharge and the shortest time to peak. Such an increase in the peak discharge and reduction in the time to peak will increase the risk of flooding and, therefore, extreme care needs to be taken before and during the implementation of PCI.