The long-term observational data of sunshine duration(SD) and diffuse radiation percentage(defined as diffuse solar radiation/total solar radiation, DRP) on sunny days during 1960–2005 were analyzed in 7 urban agglomerations and the whole of China. The results show that the sunny sunshine duration(SSD) has decreased significantly except at a few stations over northwestern China in the past 46 years. An obvious decrease of the SSD is found in eastern China, with the trend coefficients lower than-0.8. Accompanied by the SSD decline, the sunny diffuse radiation percentage(SDRP) in most stations shows obvious increasing trends during the 46 years. The averaged SDRP over China has increased 2.33%per decade, while the averaged SSD shows a decrease of-0.13 hr/day per decade. The correlation coefficient between SDRP and SSD is-0.88. SSD decreased over urban agglomerations(small to large city clusters) in the past 46 years, especially in large cities and medium cities, due to the strong anthropogenic activities and air pollution represented by aerosol option depth(AOD) and tropospheric column NO2(Tro NO2). On the regional scale, SSD has an opposite trend from SDRP during 1960 to 2005, and the variation trends of regional mean values of SSD and SDRP in southeastern China are more pronounced than those in northwestern China.
An ensemble soil moisture dataset was produced from 11 of 25 global climate model (GCM) simulations for two climate scenarios spanning 1900 to 2099; this dataset was based on an evaluation of the spatial correlation of means and trends in reference to soil moisture simulations conducted using the community land model driven by observed atmospheric forcing. Using the ensemble soil moisture index, we analyzed the dry-wet climate variability and the dynamics of the climate zone boundaries in China over this 199-year period. The results showed that soil moisture increased in the typically arid regions, but with insignificant trends in the humid regions; furthermore, the soil moisture exhibited strong oscillations with significant drought trends in the transition zones between arid and humid regions. The dynamics of climate zone boundaries indicated that the expansion of semiarid regions and the contraction of semi-humid regions are typical characteristics of the dry-wet climate variability for two scenarios in China. During the 20th century, the total area of semiarid regions expanded by 11.5% north of 30°N in China, compared to the average area for 1970-1999, but that of semi-humid regions decreased by approximately 9.8% in comparison to the average for the period of 1970-1999, even though the transfer area of the humid to the semi-humid regions was taken into account. For the 21st century, the dynamics exhibit similar trends of climate boundaries, but with greater intensity.
To evaluate the contribution of urban surface expansion to regional warming using different methods to calculate the daily mean surface air temperature(SAT), satellite-based images displaying urban surface expansion over the past 37 years(1980–2016) across China were collected for use in nested numerical experiments using the weather research and forecasting(WRF) regional climate model. The contribution of urban surface expansion to urban-related warming was determined using the daily mean SAT averages based on four time records each day(00, 06, 12, and 18 h UTC, T_4) and averages of the SAT maximum(Tmax) and minimum(Tmin)(Txn). The contribution of urban surface expansion to urban-related warming(relative value) in Beijing was 0.110°C per decade(22.8% of total warming) for T_4 and 0.094°C per decade(20.2%) for Txn. The values obtained when using T_4 were larger than those obtained when using Txn. Differences in the urban-related warming calculated using T_4 and Txncould be attributed to the smaller changing trends in Txnin the urban-surface expansion experiment, which resulted from a large changing trend in Tminand a much smaller changing trend in Tmax. The changes in the diurnal cycle of the energy budget due to urban surface expansion induced changes in the diurnal cycle of SAT, as evidenced by the four time records each day, as well as Tmaxand Tmin. This was especially true for periods of intense urban surface expansion, although the annual mean SAT calculated using Txnwas larger than that calculated using T_4. The increase in impervious area(walls, streets, etc.) due to urban surface expansion, as well as the widespread use of building materials with a large heat capacity resulted in a marked increase in ground heat flux in the daytime. This restricted the increase in SAT in the daytime, but promoted it at night. The increases in SAT due to urban surface expansion were not symmetrical, being smaller in the daytime and larger at night.
This study discusses the sensitivity of convective parameterization schemes(CPSs) in the Regional Climate Model(version 4.3)(Reg CM4.3) over East/South Asia. The simulations using different CPSs in Reg CM are compared to discover a suitable scheme for this region, as the performance of different schemes is greatly influenced by region and seasonality. Over Southeast China and the Bay of Bengal, the Grell scheme exhibits the lowest RMSEs of summer precipitation compared to observed data. Moreover, the Emanuel over land and Grell over ocean(ELGO) scheme enhances the simulation, in comparison with any single CPS(Grell/Emanuel) over Western Ghats, Sri Lanka, and Southeast India. Over the Huang–Huai–Hai Plain(3H) and Tibetan Plateau(TP) regions of China, the Tiedtke scheme simulates the more reasonable summer precipitation with high correlation coefficient and comparable amplitude. Especially, it reproduces a minimum convective precipitation bias of 8 mm d-1and the lowest RMSEs throughout the year over East/South Asia. Furthermore, for seasonal variation of precipitation, the Tiedtke scheme results are closer to the observed data over the 3H and TP regions. However, none of the CPSs is able to simulate the seasonal variation over North Pakistan(NP). In comparison with previous research, the results of this study support the Grell scheme over South Asia. However, the Tiedtke scheme shows superiority for the 3H, TP and NP regions. The thicker PBL, less surface latent heat flux, the unique ability of deep convection and the entrainment process in the Tiedtke scheme are responsible for reducing the wet bias.
