Suchergebnisse

Heat and drought are projected to increase globally but may be mitigated or exacerbated by land use/land cover (LULC) change. Here, we show that remote land-atmosphere feedbacks caused by historical European LULC change led to widespread changes in the energy and water balances, drought, and heat. Using a continental-scale bedrock-to-atmosphere model, we find that LULC change following the Soviet Union collapse and European Union formation may have substantially increased cloud cover and decreased incoming shortwave radiation in western Europe, even in locations where LULC did not change. These changes to the water and energy balances had spatially heterogeneous impacts on drought and heat, including drying in the Mediterranean and Eastern Europe. The response of the water and energy balances to remote feedbacks was lessened in areas with shallow groundwater, indicating that local- and continental-scale responses to LULC change are influenced by the coupling between the subsurface, land surface, and atmosphere.

Abstract. The disastrous July 2021 flooding event made us question the ability of current hydrometeorological tools in providing timely and reliable flood forecasts for unprecedented events. This is an urgent concern since extreme events are increasing due to global warming, and existing methods are usually limited to more frequently observed events with the usual flood generation processes. For the July 2021 event, we simulated the hourly
streamflows of seven catchments located in western Germany by combining
seven partly polarimetric, radar-based quantitative precipitation estimates
(QPEs) with two hydrological models: a conceptual lumped model (GR4H) and a
physically based, 3D distributed model (ParFlowCLM). GR4H parameters were
calibrated with an emphasis on high flows using historical discharge
observations, whereas ParFlowCLM parameters were estimated based on
landscape and soil properties. The key results are as follows. (1) With no
correction of the vertical profiles of radar variables, radar-based QPE
products underestimated the total precipitation depth relative to rain
gauges due to intense collision–coalescence processes near the surface, i.e., below the height levels monitored by the radars. (2) Correcting the vertical profiles of radar variables led to substantial improvements. (3) The probability of exceeding the highest measured peak flow before July 2021 was highly impacted by the QPE product, and this impact depended on the catchment for both models. (4) The estimation of model parameters had a
larger impact than the choice of QPE product, but simulated peak flows of
ParFlowCLM agreed with those of GR4H for five of the seven catchments. This
study highlights the need for the correction of vertical profiles of
reflectivity and other polarimetric variables near the surface to improve
radar-based QPEs for extreme flooding events. It also underlines the large
uncertainty in peak flow estimates due to model parameter estimation.