|Zusammenfassung||This thesis investigates hydro-meteorological boundary conditions in the region of Cajamarca in the northern Andes of Peru and quantifies the impact of selected resource conservation measures on the hydrology of the Ronquillo watershed. The research was undertaken as part of the research project The conservation of water and soil resources in the Chetillano and Ronquillo basins in the Northern Sierra of Peru (CASCUS). The project aims to identify opportunities for enhancing water availability and reducing soil erosion in the region of Cajamarca.
This thesis aims to contribute to the CASCUS project by strengthening the knowledge base on hydro-meteorological boundary conditions in the research area. It also seeks to advance the envisioned integrated resource management strategy by quantifying the impact of selected resource conservation measures on the hydrology of the Ronquillo watershed. In order to achieve these objectives, research was undertaken in several stages. Specifically, these stages were: (1) the exploration of the meteorological and hydrological boundary conditions, (2) the development of scenarios for the implementation of resource conservation measures, and (3) the assessment of the hydrological impact of resource conservation measures on the catchment by applying a rainfall-runoff model.
The region under investigation is characterized by a complex mountain climate marked by the interaction of a number of meteorological features, including seasonal displacement of the Intertropical Convergence Zone, orographic rainout, rain-bearing mesoscale cloud systems, El Niño Southern Oscillation (ENSO), katabatic drainage flow and local convection, all of which act on different spatial and temporal scales. The Ronquillo watershed displays strong seasonality in stream flow. During the rainy season a large portion of stream flow originates from direct runoff, which drains the watershed rapidly. The main flood formation areas are located in the middle part of the catchment, where soil and land coverage characteristics are most prone to generate surface runoff during strong rainfall. During the dry season a large portion of the discharge of the Ronquillo River originates from the soils covering the high altitude Jalca grasslands. In addition the basement rock aquifers and spring discharge significantly contribute to the dry seasonal discharge.
The main objective of the scenario development phase is to provide implementation scenarios for selected soil and water conservation techniques (SWCTs) in the Ronquillo watershed, in order to evaluate their impact on catchment hydrology by applying a rainfall-runoff model. The present study evaluates various implementation scenarios for SWCTs, which fall under the categories “earthworks,” “afforestation,” and “check dam construction.” The earthworks scenarios are developed on the basis of a decision support model. Therefore a multi-criteria evaluation procedure is used that takes into account environmental site assessment criteria such as meteorology, hydrology, topography, land use, and soil properties. Each environmental site assessment criterion is evaluated using a pair-wise comparison matrix method, known as the Analytical Hierarchy Process. Afforestation scenarios are developed for the planting of pine and eucalyptus species, based on the underlying hypotheses that existing tree coverage areas can build the nucleus for future afforestation and that primarily degraded areas will be subject to afforestation. For the implementation of check dams, two scenarios are developed. In the first, check dams are implemented in all stream channels, whereas in the second, check dams are implemented in intermittent stream channels only.
The impact of different SWCTs on the hydrology of the Ronquillo watershed is assessed using a hydrological modeling approach. Analysis undertaken with the NASIM rainfall-runoff model shows that earthworks (terraces and bund systems) and afforestation scenarios considerably impact the hydrology of the Ronquillo River. By contrast, the impact of check dam scenarios on catchment hydrology is comparatively small. The results imply that earthworks and afforestation reduce surface runoff, and thus mitigate the self-reinforcing process of surface runoff generation and subsequent soil erosion. However, this comes at the expense of a reduction in stream flow. On-site effects such as the reduction of overland flow and enhanced water availability for crop growth in situ are counterbalanced by a reduction in water availability off-site. The modeling results imply that within the framework of a water resource conservation strategy, the implementation of earthworks compared to afforestation measures is preferable, as earthworks reduce surface runoff more efficiently compared to afforestation measures, and thus have less impact on water availability downstream.