Official meteorological station data underestimate the heat stress on dairy cattle in a tropical environment

ABSTRACT The values of air temperature, relative humidity and Temperature Humidity Index (THI) of one pasture-based milk production farm and from the nearest official weather station were confronted. At the farm, data readings were recorded by an automatic weather station, every five minutes, from February 2015 to September 2016. Then, the hourly average and hourly THI were calculated. The minimum, average, and maximum daily values were selected. The same was done with data from the official hourly weather station data. The minimum and mean temperature in the meteorological station were higher than on the farm throughout the experimental period and in 16 months, respectively. The maximum temperature of the rural property was greater than that of the station in six months. Meanwhile, the minimum, average, and maximum relative humidity of the meteorological station were lower than those of the farm. The minimum THI was higher at the official station and the maximum THI was higher at the farm in every month. Finally, the number of days with a maximum THI equal to or greater than the critical THI was greater on the farm. Thus, official weather station data underestimate the heat stress.

摘要：本研究对某放牧型奶牛养殖场的气温、相对湿度及温度湿度指数（Temperature Humidity Index, THI）数据，与邻近官方气象站的对应观测数据开展比对分析。该养殖场配备自动气象站，于2015年2月至2016年9月期间以每5分钟的频率记录气象数据，随后计算得到逐小时平均值与逐小时THI，并提取每日的最小值、平均值与最大值。官方逐小时气象站数据亦采用完全一致的处理流程。在整个实验周期内，官方气象站测得的最低气温与平均气温分别高于养殖场，该差异覆盖16个月的观测时长；而该牧场的最高气温则在6个月份的周期内高于官方气象站。与此同时，官方气象站记录的最低、平均及最高相对湿度均低于养殖场。官方气象站的最低THI高于养殖场，但该牧场的最高THI在每个观测月均更高。最终，当日最高THI达到或超过临界THI的天数，在该牧场中更多。综上可见，官方气象站数据会低估热应激程度。