Precipitation cycles in the middle and lower reaches of the Yellow River （1736-2000）

Based on the long-term precipitation series with annual time resolution in the middle and lower reaches of the Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archives of the Qing Dynasty, the precipitation cycles are analyzed by wavelet analysis and the possible climate forcings, which drive the precipitation changes, are explored. The results show that： the precipitation in the middle and lower reaches of the Yellow River has inter-annual and inter-decadal oscillations like 2-4a, quasi-22a and 70-80a. The 2-4a cycle is linked with El Nino events, and the precipitation is lower than normal year in the occurrence of the El Nino year or the next year; for the quasi-22a and the 70-80a cycles, Wolf Sun Spot Numbers and Pacific Decadal Oscillation （PDO） coincide with the two cycle signals. However, on a 70-80a time scale, the coincidence between solar activity and precipitation is identified before 1830, and strong （weak） solar activity is generally correlated to the dry （wet） periods; after 1830, the solar activity changes to 80-100a quasi-century long oscillation, and the adjusting action to the precipitation is becoming weaker and weaker; the coincidence between PDO and precipitation is shown in the whole time series. Moreover, in recent 100 years, PDO is becoming a pace-maker of the precipitation on the 70-80a time scale.

Agriculture Development-induced Surface Albedo Changes and Climatic Implications Across Northeastern China

To improve the understandings on regional climatic effects of past human-induced land cover changes,the surface albedo changes caused by conversions from natural vegetation to cropland were estimated across northeastern China over the last 300 years,and its climatic effects were simulated by using the Weather Research and Forecasting (WRF) model.Essential natural vegetation records compiled from historical documents and regional optimal surface albedo dataset were used.The results show that the surface albedo decreased by 0.01-0.03 due to conversions from grassland to cropland in the Northeast China Plain and it increased by 0.005-0.015 due to conversions from forests to cropland in the surrounding mountains.As a consequence,in the Northeast China Plain,the surface net radiation increased by 4-8 W/m 2,2-5 W/m 2,and 1-3 W/m 2,and the climate was therefore warmed by 0.1℃-0.2℃、0.1℃-0.2℃、 0.1℃-0.3 ℃ in the spring,autumn and winter,respectively.In the surrounding mountain area,the net radiation decreased by less than 1.5 W/m 2,and the climate was therefore cooled too slight to be detected.In summer,effects of surface albedo changes on climate were closely associated with moisture dynamics,such as evapotranspiration and cloud,instead of being merely determined by surface radiation budget.The simulated summer climatic effects have large uncertainties.These findings demonstrate that surface albedo changes resulted in warming climate effects in the non-rainy seasons in Northeast China Plain through surface radiation processes while the climatic effects in summer could hardly be concluded so far.

Farmland dataset reconstruction and farmland change analysis in China during 1661-1985

This research reconstructs China＇s provincial farmland dataset in the last 300 years （1661-1985） by applying factor correction, citing replacement, linear interpolation, cohesion and contrast, man-land relationship test, farming trend test, provincial administrative area adjustment, etc. on available farmland data based on China＇s current provincial administrative boundary. Based on this dataset, a quantitative analysis has been applied to study the farm- land amount and its change Characteristics at both national and provincial level. Three con- clusions are derived： （1） Along with the rapid population growth, national farmland amount has increased by about 320% in the last 300 years from 424,480 km2 in the early Qing Dy- nasty to 1,368,600 km2 in 1985. Comparing with global and national farmland datasets, in terms of the overall trend of national farmland growth, very low deviation exists but significant variances do appear for some provinces. （2） At the beginning of the Qing Dynasty, China＇s farming activities mainly existed in the Yangtze River Plain, the North China Plain, the Guanzhong Basin and the Yinchuan Plain. Thereafter, reclamation activities expanded to outer agricultural areas. Regarding of the growth rate, national farmland increase can be divided into five phases. National policy, disasters, wars, and economic development, are the main factors affecting farmland changes. （3） Significant regional variances exist in farmland changes. In the space shaped by the average farmland amount and the average annual change rate of farmland, the nation can be divided into six areas.