D. Wiberg

WATCH: Current Knowledge of the Terrestrial Global Water Cycle

AbstractWater-related impacts are among the most important consequences of increasing greenhouse gas concentrations. Changes in the global water cycle will also impact the carbon and nutrient cycles and vegetation patterns. There is already some evidence of increasing severity of floods and droughts and increasing water scarcity linked to increasing greenhouse gases. So far, however, the most important impacts on water resources are the direct interventions by humans, such as dams, water extractions, and river channel modifications. The Water and Global Change (WATCH) project is a major international initiative to bring together climate and water scientists to better understand the current and future water cycle. This paper summarizes the underlying motivation for the WATCH project and the major results from a series of papers published or soon to be published in the Journal of Hydrometeorology WATCH special collection. At its core is the Water Model Intercomparison Project (WaterMIP), which brings togeth...

Assessing the implications of water harvesting intensification on upstream–downstream ecosystem services: A case study in the Lake Tana basin

Water harvesting systems have improved productivity in various regions in sub-Saharan Africa. Similarly, they can help retain water in landscapes, build resilience against droughts and dry spells, and thereby contribute to sustainable agricultural intensification. However, there is no strong empirical evidence that shows the effects of intensification of water harvesting on upstream-downstream social-ecological systems at a landscape scale. In this paper we develop a decision support system (DSS) for locating and sizing water harvesting ponds in a hydrological model, which enables assessments of water harvesting intensification on upstream-downstream ecosystem services in meso-scale watersheds. The DSS was used with the Soil and Water Assessment Tool (SWAT) for a case-study area located in the Lake Tana basin, Ethiopia. We found that supplementary irrigation in combination with nutrient application increased simulated teff (Eragrostis tef, staple crop in Ethiopia) production up to three times, compared to the current practice. Moreover, after supplemental irrigation of teff, the excess water was used for dry season onion production of 7.66 t/ha (median). Water harvesting, therefore, can play an important role in increasing local- to regional-scale food security through increased and more stable food production and generation of extra income from the sale of cash crops. The annual total irrigation water consumption was ~4%-30% of the annual water yield from the entire watershed. In general, water harvesting resulted in a reduction in peak flows and an increase in low flows. Water harvesting substantially reduced sediment yield leaving the watershed. The beneficiaries of water harvesting ponds may benefit from increases in agricultural production. The downstream social-ecological systems may benefit from reduced food prices, reduced flooding damages, and reduced sediment influxes, as well as enhancements in low flows and water quality. The benefits of water harvesting warrant economic feasibility studies and detailed analyses of its ecological impacts.

Climate variability and its impacts on water resources in the Upper Indus Basin under IPCC climate change scenarios

The output of a regional climate model (RCM), providing regional climate for impact studies (PRECIS), is used as input data to the hydrological model to produce inflow projections at the Tarbela Reservoir on the Indus River. Maximum temperature, minimum temperature and precipitation are investigated for possible climate change in the region. The hydrological model was calibrated for the 1995-2004 period and validated for the 1990-1994 period with almost 90% efficiencies. The projections of inflow to the Tarbela Reservoir show that there is an overall increase of 59.42% and 34.27% to the Tarbela Reservoir during the period of 2040-2069 under the A2 and the B2 scenarios, respectively. There will be much more water available in the future, with the highest inflow and comparatively more water shortage noted in the 2020s under the A2 scenario. Finally, the impacts of changing climates on the operation of Tarbela Dam are investigated.

Sustainable Agriculture in China: Estimation and Reduction of Nitrogen Impacts

In this chapter we present an integrated model for long term and geographically explicit planning of agricultural activities to meet demands under resource constraints and ambient targets. Environmental, resource and production feasibility indicators permit estimating impacts of agricultural practices on environment to guide agricultural policies regarding production allocation, intensification, and fertilizer application while accounting for local constraints. Physical production potentials of land are incorporated in the model, together with demographic and socio-economic variables and behavioral drivers to reflect spatial distribution of demands and production intensification levels. The application of the model is demonstrated with a case study of nitrogen accounting at the level of China counties. We discuss current intensification trends and estimate the ranges of agricultural impacts on China’s environment under plausible pollution mitigation scenarios with a particular focus on nitrogen sources and losses.