Lucas Menzel

Coping with variability and change: Floods and droughts

Floods and droughts are natural phenomena for which the risks of occurrence are likely to continue to grow. Increasing levels of exposure and insufficient adaptive capacity are among the factors responsible for the rising vulnerability. The former is conditioned by anthropopressure (e.g., economic development of flood-prone areas) and adverse effects of climate change; scenarios for future climates indicate the possibility of amplified water-related extremes. This article presents the current situation of coping with extreme hydrological events within the pressure-state-response framework. Among promising response strategies, the role of forecast and warning, and of watershed management are reviewed. Sample success stories and lessons learnt related to hydrological extremes are given and policy implications discussed.

Modelling canopy resistances and transpiration of grassland

Abstract Lysimeter measurements have been used in an inverted form of the Penman-Monteith equation to calculate daily values of canopy resistances for dense and dry plant cover. The analysis of the relationship between the calculated data and a series of environmental variables showed that canopy resistances of the investigated grassland can be expressed as non-linear functions of the air temperature, leaf area index and soil moisture deficit. After linearization of these empirical functions the selected variables have been combined in a multiple regression model which was adopted as a submodel for the Penman-Monteith equation. Daily and hourly modelled canopy resistances have been used to calculate transpiration for periods with various environmental conditions. The results show that the difference between calculated and measured daily transpiration is in the range of 5 %. Hourly predicted transpiration rates are able to explain approximately 78 % of the variance of measured data.

Natural flood reduction strategies – a challenge

Abstract Flood hazard and vulnerability to floods tend to increase in many areas, due to changes in socio‐economic, and physical – especially climatic – systems. Therefore, increasing attention is being paid to upgrading flood protection systems. As in many vulnerable areas sufficient flood protection cannot be reached with the help of structural means only, further flood damage reduction via non‐structural measures is advisable. The most essential principles in natural flood reduction strategies are illustrated by the slogans “keep water where it falls” and “give rivers their floodplains back”, both being widely discussed in Germany, especially after the destructive flooding of August 2002. Examples of implementation of natural flood reduction strategies are presented.