The extreme floods of recent years underline the urgency of studying long-term changes of floods and their driving processes. This paper reports results on this issue obtained within the framework of subproject 6 of the DFG research group SPATE (Space-Time Dynamics of Extreme Floods). The analyses use an extensive dataset of flood observations at rivers and complementary information to determine and explain significant changes in flood probabilities. The data show that the flood-rich periods of the last 500 years in Europe have been significantly colder than usual. Over the last 60 years, the number of flood-rich periods in north-western Europe has increased. This increase is due to more intense precipitation. In medium-sized and large catchments of southern and eastern Europe, on the other hand, lower soil moisture and less snow cover have led to decreasing flood probabilities. These results are intended as a basis for more reliable design flood estimates in a changing world.

Permafrost is an important factor affecting soil hydrology in cold regions, while the effects of permafrost on temporal changes in soil water content largely remain unknown. Here, based on the calibrated Climate Change Initiative (CCI) soil moisture products using field observation soil water data at 5 cm depth from 8 representative sites, we examined changing trends of climate conditions and soil water contents during 1986-2016 between the permafrost and permafrost-free sites on the Qinghai-Tibetan Plateau (QTP). We found that all the sites have been experienced continuous warming during this period. Soil water contents showed significant increasing or decreasing trends at three of the four permafrost-free sites, but there were no significant increasing or decreasing changes at all the four permafrost sites. In addition, the Mann-Kendall (M K) test showed that there were 2 change-points in soil water content for the sites with the active layer thickness was about 2 m, while the sites with active layer thickness larger than 3 m and permafrost-free sites showed 3-5 change-points, indicating that the soil water contents in areas with shallower active layer showed smaller changes. The different changing trends and change-points between permafrost and permafrost-free sites were associated with the existence of permafrost and active layer thickness. Although soil water contents can be affected by many factors, our results suggested that permafrost existence can affect interannual changes in soil water contents, and permafrost degradation including increasing active layer thickness and disappearance of permafrost may decrease ecosystem resilience in the face of climate change.

In order to describe the means, variability and trends of the aerosol radiative effects on the southwest Atlantic coast of Europe, 11 years of aerosol light scattering (sigma(sp)) and 4 years of aerosol light absorption (sigma(sp)) are analyzed. A 2006-2016 trend analysis of sigma(sp) for D < 10 mu m indicates statistically significant trends for March, May-June and September-November, with a decreasing trend ranging from -1.5 to - 2.8 Mm(-1)/year. In the 2009-2016 period, the decreasing trend is only observed for the months of June and September. For scattering Angstrom exponent (SAE) there is an increasing trend during June with a rate of 0.059/year and a decreasing trend during October with - 0.060/year. The trends observed may be caused by a reduction of Saharan dust aerosol or a drop in particle loading in anthropogenic influenced air masses. The relationship between SAE and absorption Angstrom exponent is used to assess the aerosol typing. Based on this typing, the sub-micron particles are dominated by black carbon, mixed black and brown carbon or marine with anthropogenic influences, while the super-micrometer particles are desert dust and sea spray aerosol. The mean and standard deviation of the dry aerosol direct radiative effect at the top of the atmosphere (DRETOA) are -4.7 +/- 4.2 W m(-2). DRETOA for marine aerosol shows all observations more negative than - 4 W m(-2 )and for anthropogenic aerosol type, DRETOA ranges from -5.0 to -13.0 W m(-2). DRETOA of regional marine aerosol ranges from -3 to -7 W m(-2), as it consists of a mixture of sea salt and anthropogenic aerosol. The variability in DRETOA is mainly dependent on AOD, given that variations in backscatter fraction and the single scattering albedo tend to counteract each other in the radiative forcing efficiency equation. The results shown here may help in interpretation of satellite retrieval products and provide context for model evaluation.

The scientific community has widely reported the impacts of climate change on the Central Himalaya. To qualify and quantify these effects, long-term land surface temperature observations in both the daytime and nighttime, acquired by the Moderate Resolution Imaging Spectroradiometer from 2000 to 2017, were used in this study to investigate the spatiotemporal variations and their changing mechanism. Two periodic parameters, the mean annual surface temperature (MAST) and the annual maximum temperature (MAXT), were derived based on an annual temperature cycle model to reduce the influences from the cloud cover and were used to analyze their trend during the period. The general thermal environment represented by the average MAST indicated a significant spatial distribution pattern along with the elevation gradient. Behind the clear differences in the daytime and nighttime temperatures at different physiographical regions, the trend test conducted with the Mann-Kendall (MK) method showed that most of the areas with significant changes showed an increasing trend, and the nighttime temperatures exhibited a more significant increasing trend than the daytime temperatures, for both the MAST and MAXT, according to the changing areas. The nighttime changing areas were more widely distributed (more than 28%) than the daytime changing areas (around 10%). The average change rates of the MAST and MAXT in the daytime are 0.102 degrees C/yr and 0.190 degrees C/yr, and they are generally faster than those in the nighttime (0.048 degrees C/yr and 0.091 degrees C/yr, respectively). The driving force analysis suggested that urban expansion, shifts in the courses of lowland rivers, and the retreat of both the snow and glacier cover presented strong effects on the local thermal environment, in addition to the climatic warming effect. Moreover, the strong topographic gradient greatly influenced the change rate and evidenced a significant elevation-dependent warming effect, especially for the nighttime LST. Generally, this study suggested that the nighttime temperature was more sensitive to climate change than the daytime temperature, and this general warming trend clearly observed in the central Himalayan region could have important influences on local geophysical, hydrological, and ecological processes.