Diurnal surface temperature difference index derived from ground-based meteorological measurements for assessment of moisture availability

Droughts have become widespread in the Northern Hemisphere, including in China, where they have affected farmland resources on the Loess Plateau. Given this background, we proposed a new index, the Normalized Day-Night Surface Temperature Index (NTDI), to estimate moisture availability (m_a), defined as the ratio of actual to reference evapotranspiration. The NTDI is defined as the ratio of the difference between the maximum daytime surface temperature and the minimum nighttime surface temperature, to the difference between the maximum and minimum surface temperatures estimated from meteorological data by applying energy balance equations.To calculate the index, we used data of 20 clear-sky meteorological observations made during the 2005 growing season at a natural grassland station in the Liudaogou River basin on the Loess Plateau. The NTDI showed a significant inverse exponential correlation with m_a (R² = 0.97, p < 0.001), whereas the numerator of the index (the maximum daytime surface temperature minus the minimum nighttime surface temperature) was only weakly correlated with m_a (R² = 0.24, p = 0.03). This result indicates that normalization relative to the index denominator (maximum surface temperature − minimum surface temperature) dramatically improved the accuracy of the estimate.     

M5 model tree based modelling of reference evapotranspiration

This paper investigates the potential of M5 model tree based regression approach to model daily reference evapotranspiration using climatic data of Davis station maintained by California irrigation Management Information System (CIMIS). Four inputs including solar radiation, average air temperature, average relative humidity, and average wind speed whereas reference evapotranspiration calculated using a relation provided by the CIMIS was used as output. To compare the performance of M5 model tree in predicting the reference evapotranspiration, FAO–56 Penman–Monteith equation and calibrated Hargreaves–Samani relation was used. A comparison of results suggests that M5 model tree approach works well in comparison to both FAO–56 and calibrated Hargreaves–Samani relations. To judge the generalization capability of M5 model tree approach, model created by using the Davis data set was tested with the datasets of four different sites. Results from this part of the study suggest that M5 model tree could successfully be employed in modeling the reference evapotranspiration. Further, sensitivity analysis with M5 model tree approach suggests the suitability of solar radiation, average air temperature, average relative humidity, and average wind speed as input parameters to model the reference evapotranspiration Copyright © 2009 John Wiley & Sons, Ltd.     

青藏高原近30年气候变化趋势

以1971~2000年青藏高原77个气象台站的观测数据 (最低、最高气温,日照时数,相对湿度,风速和降水量) 为基础,应用1998年FAO推荐的Penman-Monteith模型,并根据我国实际状况对其辐射项进行修正,模拟了青藏高原1971~2000年的最大可能蒸散,并由Vyshotskii模型转换为干燥度,力求说明近30年青藏高原的气候变化趋势,以及干湿状况的空间分布。应用线性回归法计算变化趋势,并用Mann-Kendall方法进行趋势检验。结果表明：青藏高原近30年气候变化的总体特征是气温呈上升趋势,降水呈增加趋势,最大可能蒸散呈降低趋势,大多数地区的干湿状况有由干向湿发展的趋势。气候因子与地表干湿状况间并不是线性关系,存在很大的不确定性。     

中国荒漠化潜在发生范围的修订

为了客观反映中国荒漠化发生区域,按照联合国防治荒漠化《公约》的定义,利用1950-1990年间全国671个气象站的长时间序列气象数据,分别采用Thornthwaite和Penman计算可能蒸散量的方法计算了湿润指数的分布,然后根据中国气候区划和中国植被区划以及中国荒漠化发生的特点等对计算结果进行了调整,对中国荒漠化潜在发生范围进行了修订,明确了荒漠化各气候类型区的地理涵义。研究结果表明：①《公约》定义的荒漠化潜在发生范围及各气候类型区的划分标准不完全适用于中国。②中国的荒漠化发生在极干旱区、干旱区、半干旱区和亚湿润干旱区。极干旱区对应极旱荒漠,干旱区对应典型荒漠、草原化荒漠以及荒漠草原,半干旱区对应典型草原,亚湿润干旱区对应草甸草原中偏干旱的部分。③修订后中国荒漠化潜在发生范围总面积约4 524 089.1 km²,约占国土总面积的47.1％,其中亚湿润干旱区、半干旱区、干旱区和极干旱区分别占12.6％、28.8％、34.4％和24.2％。荒漠化潜在发生范围修订后比修订前增加1 207 056.9 km²,其中亚湿润干旱区面积减少,半干旱区、干旱区和极干旱区面积增加。     

用多变量灰色预测模型模拟预测参考作物蒸散量的研究

当观测资料的数据量少而又存在多个相互影响或关联的变量时,常用的灰色预测模型GM（1,1）不能全面考虑多个变量。为此,采用自适应MGM（1,n）模型—多变量灰色预测模型,较好地解决了这一问题。针对一些地区气象数据较少甚至缺失的情况,以内蒙古正蓝旗的气象资料用Penman-Monteith计算的参考作物蒸散量（ET0）为研究对象,运用灰色系统理论建立MGM（1,3）模型,模拟预测参考作物蒸散量变化规律,并与GM（1,1）模型和BP神经网络模型比较,结果表明MGM（1,3）模型有较好的预测效果。     

参考作物蒸散量的多种计算方法及其结果的比较

分别用 FAO Penman- Monteith公式 (模型 1 )、FAO Penman 修正式 (模型 2 )和国内Penman修正式 (模型 3)计算了泰安和西峰两地的参考作物蒸散量 ,对 3种方法的计算结果进行了比较 .模型 1得到的参考作物蒸散量大于后 2种模型 ,导致不同模型计算偏差的原因是 3种模型各自选用了不同的辐射项和动力项计算式 ,且计算偏差随季节和地理条件而变 .建议计算区域参考作物蒸散量用模型 1 ,计算单站逐日参考作物蒸散量 3种模型都可用 .     

奈曼沙地春小麦蒸散量及其分析

运用波文比-能量平衡法和大型蒸渗仪对沙地春小麦的蒸散量进行了连续的测定和估算,并对由于降雨和灌溉所引起的土壤有效水分变化与沙地春小麦蒸散量之间的相关关系进行了初步探讨。结果表明:①春小麦蒸散量在降水或灌溉后1~2 d最大,然后逐渐下降,说明春小麦的蒸散速度受土壤有效水分含量的影响;②春小麦出苗前和生长初期,蒸散以地表蒸发为主,蒸散量较小,感热通量和土壤热通量较大;随着时间推移,L AI(叶面积系数)逐渐增大,由于作物遮蔽,感热通量和土壤热通量减小,潜热通量对净辐射贡献增大;③测定期间,波文比在早晨日出前(5:00)达到最大,至下午15:00左右下降为最小,然后开始增大至次日凌晨;④应用波文比-能量平衡法估测的沙地春小麦蒸散量与大型蒸渗仪的测定值一致性较好,相关系数R²为0.9055。     

Late quaternary paleoclimatic reconstructions for interior Alaska based on paleolake-level data and hydrologic models

Hydrologic models are developed for two lakes in interior Alaska to determine quantitative estimates of precipitation over the past 12,500 yrs. Lake levels were reconstructed from core transects for these basins, which probably formed prior to the late Wisconsin. Lake sediment cores indicate that these lakes were shallow prior to 12,500 yr B.P. and increased in level with some fluctuation until they reached their modern levels 4,000-8,000 yr B.P. Evaporation (E), evapotranspiration (ET), and precipitation (P) were adjusted in a water-balance model to determine solutions that would maintain the lakes at reconstructed levels at key times in the past (12,500, 9,000 and 6,000 yr B.P.). Similar paleoclimatic solutions can be obtained for both basins for these times. Results indicate that P was 35-75% less than modern at 12,500 yr B.P., 25-45% less than modern at 9,000 yr B.P. and 10-20% less than modern at 6,000 yr B.P. Estimates for E and ET in the past were based on modern studies of vegetation types indicated by fossil pollen assemblages. Although interior Alaska is predominantly forested at the present, pollen analyses indicate tundra vegetation prior to about 12,000 yr B.P. The lakes show differing sensitivities to changing hydrologic parameters; sensitivity depends on the ratio of lake area (AL) to drainage basin (DA) size. This ratio also changed over time as lake level and lake area increased. Smaller AL to DA ratios make a lake more sensitive to ET, if all other factors are constant.     

基于地表能量平衡与SCS模型的祁连山水源涵养能力研究

基于区域水量平衡,利用地表能量平衡的原理计算陆地实际蒸散发量,采用SCS模型计算地表径流量,提出了一种定量评估区域水源涵养量的实用方法。利用该方法和GIS软件平台,结合1982-2003年遥感数据和对祁连山水源涵养重要区水源涵养能力强弱的空间分布及其变化规律进行了计算和分析。结果表明:(1)祁连山山地水源涵养重要区内水源涵养能力最强的区域为中部和东南部地区,而西部地区涵养水源的能力相对较弱;(2)祁连山山地水源涵养重要区内中部和靠东南部的水源涵养能力减弱比较明显,特别是以门源回族自治县为中心,形成了水源涵养能力持续减弱带。