Land use change and impacts on watersheds of large urban lakes (Project 3)

This project was characterized the biological and physical components of three watersheds of Laguna de Bay [Philippines] with the intention of identifying critical areas within the study area through vulnerability assessment. Major activities included land cover/land use characterization using satellite images covering two decades and six time periods, spatio-temporal land cover/land use change analysis, and assessment of the hydrologic regime through the installation of automatic weather system (AWS) and water level (AWLS) instruments in various sites of the study area. The hydrologic and land use/land cover analysis became the basis for identifying criteria of watershed health, namely: hydrologic response, biodiversity and connectivity, socio-ecological system, hazards assessment, and ecological footprint analysis.All these criteria are anchored on land use/land cover dynamics. This project used the GAME [Geographic Information System-Based Assessment Monitoring and Evaluation] Model gridding system for vegetation assessment, ArcSWAT for modeling the hydrologic response of the watershed to land management practices, and unit hydrographs from storm and heavy rainfall events for vulnerability assessment. Results of the biophysical assessment show that majority of the watershed exhibit Macolod soil (Undifferentiated) series, and the geology is mostly under Pliocene-Quaternary. Analysis of the land cover changes reveal that Tigbi has the largest increase of built-up area from 2003 to 2010, but it also has the largest increase in area for closed forest (387.57 ha to 628.86 ha). In terms of the overall area of the watersheds, only the closed forests and cultivated lands (annual copy) have decreased, while the rest of the other land classes reported in increase in area. The vegetation surveys showed that Family Moraceae has the most number of representatives for each family (26 species), while Fabaceae and Sapindacceae have the lowest number (nine species each). Results from the key information interviews showed that farmers within the boundary of MFR use traditional agroforestry practices. The analysis of vulnerability to landslide showed that in Cambantoc Watershed. only about 7% or 132 ha are found to ave high vulnerability to landslide. Most of these are located in Brgy. [village] Batong Malake (55 ha) in Los Baños and in Brgy Bitin (28 ha) in Bay. For the Molawin-Dampalit Watershed, about 4% or 149 ha are highly vulnerable to landslide. These are situated mostly in Brgy Anos (66 ha), Brgy Bambang (53 ha), and Brgy Batong Malake (22 ha) in Los Baños Large portions of the moderate vulnerable areas are observed in the same barangays with high vulnerabilities in Los Baños including Bagong Silang (128 ha) and in Brgy Santa Cruz (126 ha) in Bay. Meanwhile for Tigbi Watershed, an approximate of 8% or 157 ha are classified as high and most of the barangays affected are Brgy Bambang (76 ha) and Brgy Lalakay (76 ha) in Los Baños. Moderate areas to landslide are situated mostly in Brgy. Puting Lupa (246 ha) in Calamba City and in Brgy Lalakay (275 ha) in Los Baños. Flood-prone areas were identified in In Cambantoc Watershed, about 20% or 395 ha are classified under high vulnerable areas with Brgy Maitim (99 ha) and Santo Domingo (164 ha) having the largest areas prone to flooding in Bay. Meanwhile in Molawin-Dampalit Watershed, approximately 26% or around 1,071 ha have high vulnerabilities. Mostly these are located in Brgy. Maahas (288 ha), Brgy Batong Malake (221 ha), Brgy Putho Tuntungin (170 ha), and Brgy Anos (128 ha in the municipality of Los Baños. As for the Tigbi Watershed,about 20% or 378 ha are vulnerable to flooding and these are mostly located in Brgy Sucol (124 ha). Brgy Bagong Kalsada (47 ha), Brgy Masili (42 ha), and Brgy Pansol (41 ha) in Calamba City and Lalakay (115 ha) in Los Baños. On the other hand, Cambantoc (approx. 9% or 166 ha) and Molawin-Dampalit (approx 11% or 472 ha) are vulnerable to drought. These are located in barangays Santo Domingo (76 ha), Paciano Rizal (43 ha), and Maitim (35 ha) in Los Baños in Cambantoc. Meanwhile in the Molawin-Dampalit Watershed, affected areas are in Brgy Batong Malake (93 ha), Brgy Mayondon (84 ha), and Brgy Bayog (76 ha) in Los Baños while part of Brgy Paciano Rizal (38 ha) is also classified under high vulnerabilities. However, in Tigbi Watershed, only 5% or roughly 90% ha are affected with high vulnerability to drought. Brgy Sucol (39 ha) has the highest vulnerable areas to drought in Calamba City while Brgy Lalakay (25 ha) in Los Baños. Assessment of the hydrologic behavior of the study areas using SWAT [Soil and Water Assessment Tool] modeling suggest that water yield and surface runoff may be substantial. In other words, the water balance ratios indicate taht majority of the precipitation goes to streamflow while majority of the total flow is composed of surface runoff. Results of this study can be used in the development of a Watershed Vulnerability Index (WVI) that is based to a large extent on land use/land cover change dynamics using the criteria listed earlier. The WVI can be a useful basis for policy actions on a watershed scale.