Monthly Means Of Daily Minimum Temperature (C) June

Minimum (Night-Time) temperatures, there is abundant evidence for the climatic limitation of crop distributions to be described by minimum temperatures, from a perspective of crop survival (on Frost for tolerance levels of crops). Many subtropical crops may be killed at 5 degree Celsius already through chilling injury, even in the absence of frost (Chang, 1968). High minima increase respiration loss, thereby decreasing net photosynthesis. Daily minimum temperature time series were derived from over 970 qualifying temperature stations` quality controlled daily records for the 50 year period 1950 - 1999. From these time series, 50 years of daily values of minimum temperatures were generated at each of 429 700 one arc minute (i.e. 1.7 km x 1.7 km) raster points covering South Africa, using regional and seasonal lapse rate and infilling/data extension techniques developed by Schulze and Maharaj (2004). Note that in the generation of daily minimum temperatures no account could be taken of cold air drainage into hollows or valleys, which can take place from surrounding higher-lying areas through radiative cooling during calm, stable clear night conditions. Reasons for this are provided in Schulze and Maharaj (2004). From these daily values, monthly means of daily minimum temperatures, as well as standard deviation of daily minimum temperatures for each month of the year, could be computed for purposes of mapping and production of statistics which are tabulated for Swaziland, Lesotho and for each of the nine provinces of the RSA. This approach to mapping minimum temperatures is thus fundamentally different to that used in the previous `South African Atlas of Agrohydrology and Climatology` (Schulze, 1997), in being much more physically based.

最低（夜间）气温：已有充分证据表明，作物分布的气候限制可通过最低气温加以阐释，其核心视角为作物存活（基于作物的霜冻耐受等级）。诸多亚热带作物即便未遭遇霜冻，也可能在5摄氏度时因冷害死亡（Chang，1968）。较高的夜间最低气温会加剧呼吸消耗，进而降低净光合速率。1950-1999年这50年间，研究团队从970余个符合标准的气象站经过质量控制的逐日气温记录中，提取得到日最低气温时间序列。基于上述时间序列，研究人员借助Schulze与Maharaj（2004）提出的区域-季节递减率及插值/数据延拓技术，在覆盖南非的429700个1弧分（即1.7km×1.7km）栅格点上生成了1950-1999年共50年的日最低气温序列。需注意：在生成日最低气温数据时，未考虑静稳晴朗夜间由周边高地通过辐射冷却形成的冷空气向洼地或山谷汇流的过程，相关原因详见Schulze与Maharaj（2004）的研究。基于上述日最低气温数据，可计算得到各月日最低气温的月平均值以及年各月日最低气温的标准差，用于制图及统计分析；相关统计结果已针对斯威士兰、莱索托以及南非共和国（RSA）的9个省份分别制表。本次日最低气温制图所采用的方法，与此前《南非农业水文与气候图集》（Schulze，1997）中使用的方法存在本质区别，其物理机制更为严谨。