Forests are undergoing significant changes throughout the globe. These changes can modify water, energy, and carbon balance of the land surface, which can ultimately affect climate. We utilize satellite data to quantify the potential and actual impacts of forest change on land surface temperature (LST) from 2003 to 2013. The potential effect of forest change on temperature is calculated by the LST difference between forest and nearby nonforest land, whereas the actual impact on temperature is quantified by the LST trend difference between deforested (afforested) and nearby unchanged forest (nonforest land) over several years. The good agreement found between potential and actual impacts both at annual and seasonal levels indicates that forest change can have detectable impacts on surface temperature trends. That impact, however, is different for maximum and minimum temperatures. Overall, deforestation caused a significant warming up to 0.28 K/decade on average temperature trends in tropical regions, a cooling up to −0.55 K/decade in boreal regions, a weak impact in the northern temperate regions, and strong warming (up to 0.32 K/decade) in the southern temperate regions. Afforestation induced an opposite impact on temperature trends. The magnitude of the estimated temperature impacts depends on both the threshold and the data set (Moderate Resolution Imaging Spectroradiometer and Landsat) by which forest cover change is defined. Such a latitudinal pattern in temperature impact is mainly caused by the competing effects of albedo and evapotranspiration on temperature. The methodology developed here can be used to evaluate the temperature change induced by forest cover change around the globe.

Abstract

A set of daily precipitation data from 1958 to 2007 was analysed for the area in and around the Three Gorges Reservoir Region. Annual and monthly precipitation, number of rainy days (NRDs), precipitation intensity (INT), and seven indices of extreme precipitation and drought were examined. Correlation between circulation indices and climate parameters was analysed. Significant decreases were detected in spring, fall, winter and annual NRDs, while significant increases were found in precipitation INT. Inter-decadal changes are obvious, it was wettest in the early 1980s, and dry in the first few years and after 1990. No significant changes are found in extreme precipitation/drought events, but a closer examination suggested they might become more frequent after 1980. Precipitation totals and days of extreme precipitation in a specific period were found to be negatively correlated with western North Pacific Monsoon Index (WNPMI); positively correlated with summer average of index of the ridge of western Pacific subtropical high; and positively correlated with summer average of index of INT of western Pacific subtropical high and the winter-summer difference of Tibetan Plateau (TP) index. These links were significant but not strong, which might manifest the characteristics of Three Gorges Area as a transition zone, where precipitation is influenced by multiple systems. Regional management should be more careful to adjust to these changes.

The pattern of timberline distribution on mountain ranges world-wide is related to global factors. The basic factor is temperature and the amount of radiation, which falls with increasing distance from the equator. Additionally, this basic relationship is overlaid by the specific features of the type of climate on the massif (degree of continentality or oceanity) and the mass-elevation effect. In the Carpathians, the mass elevation effect seems to have bigger impact on the location of timberline (R 2 = 0.71, p = 0.00) than their latitudinal location (R 2 = 0.56, p = 0.00). The timberline altitude changes by 70 m a.s.l. (±20 m) with each degree of latitude. The influence of the type of the climate is complex and it is not clearly visible due to past and recent human impact.

Land use changes affect the surface radiative budget and energy balance by changing the surface albedo, which generates radiative forcing, impacting the regional and global climate. To estimate the effect of land use changes on the surface albedo and climate change in a mountainous area with complex terrain, we obtained MODIS data, identified the spatial–temporal characteristics of the surface albedo caused by land use changes, and then calculated the radiative forcing based on solar radiative data and the surface albedo in the Qinling-Daba mountains from 2000 to 2015. The correlation between the land use changes and the radiative forcing was analyzed to explore the climate effects caused by land use changes on a kilometer-grid scale in the Qinling-Daba mountains. Our results show that the primarily land use changes were a decrease in the cultivated land area and an increase in the construction land area, as well as other conversions between six land use types from 2000 to 2015. The land use changes led to significant changes in the surface albedo. Meanwhile, the radiative forcing caused by the land use had different magnitudes, strengths, and occurrence ranges, resulting in both warming and cooling climate change effects.

No abstract

The Greater Khingan Mountains (Daxinganling) are China's important ecological protective screen and also the region most sensitive to climate changes. To gain an in-depth understanding and reveal the climate change characteristic in this high-latitude, cold and data-insufficient region is of great importance to maintaining ecological safety and corresponding to global climate changes. In this article, the annual average temperature, precipitation and sunshine duration series were firstly constructed using tree-ring data and the meteorological observation data. Then, using the climate tendency rate method, moving-t-testing method, Yamamoto method and wavelet analysis method, we have investigated the climate changes in the region during the past 307 years. Results indicate that, since 1707, the annual average temperature increased significantly, the precipitation increased slightly and the sunshine duration decreased, with the tendency rates of 0.06℃/10a, 0.79 mm/10a and-5.15 h/10a, respectively (P≤0.01). Since the 21st century, the period with the greatest increase of the annual average temperature (also with the greatest increase of precipitation) corresponds to the period with greatest decrease of sunshine duration. Three sudden changes of the annual average temperature and sunshine duration occurred in this period while two sudden changes of precipitation occurred. The strong sudden-change years of precipitation and sunshine duration are basically consistent with the sudden-change years of annual average temperature, suggesting that in the mid-1860s, the climatic sudden change or transition really existed in this region. In the time domain, the climatic series of this region exhibit obvious local variation characteristics. The annual average temperature and sunshine duration exhibit the periodic variations of 25 years while the precipitation exhibits a periodic variation of 20 years. Based on these periodic characteristics, one can infer that in the period from 2013 to 2030, the temperature will be at a high-temperature stage, the precipitation will be at an abundant-precipitation stage and the sunshine duration will be at an less-sunshine stage. In terms of spatial distribution, the leading distribution type of the annual average temperature in this region shows integrity, i.e., it is easily higher or lower in the whole region; and the second distribution type is more (or less) in the southwest parts and less (or more) in the northeast parts. Precipitation and sunshine duration exhibit complex spatial distribution and include four Keywords: climate change; temporal and spatial characteristics; northern Greater Khingan Mountains; sudden change test; period analysis

The extreme Arctic sea ice minima in the 21st century have been attributed to multiple factors, such as anomalous atmospheric circulation, excess solar radiation absorbed by open ocean, and thinning sea ice in a warming world. Most likely it is the combination of these factors that drive the extreme sea ice minima, but it has not been quantified, how the factors rank in setting the conditions for these events. To address this question, the sea ice budget of an Arctic regional sea ice-ocean model forced by atmospheric reanalysis data is analyzed to assess the development of the observed sea ice minima. Results show that the ice area difference in the years 2012, 2019, and 2007 is driven to over 60% by the difference in summertime sea ice area loss due to air-ocean heat flux over open water. Other contributions are small. For the years 2012 and 2020 the situation is different and more complex. The air-ice heat flux causes more sea ice area loss in summer 2020 than in 2012 due to warmer air temperatures, but this difference in sea ice area loss is compensated by reduced advective sea ice loss out of the Arctic Ocean mainly caused by the relaxation of the Arctic Dipole. The difference in open water area in early August leads to different air-ocean heat fluxes, which distinguishes the sea ice minima in 2012 and 2020. Further, sensitivity experiments indicate that both the atmospheric circulation associated with the Arctic Dipole and extreme storms are essential conditions for a new low record of sea ice extent.