Evapotranspiration estimation of Platycladus orientalis in Northern China based on various models

Platycladus orientalis is one of the most popular afforestation species and greening species for water management in arid and semi-arid regions of northern China. We applied various models to estimate and validate artificial P. orientalis forest evapotranspiration features with the goal of accurately estimating the water use of a P.orientalis plantation. The American Society of Civil Engineers Evapotranspiration–Penman–Monteith model（APM） and FAO56–Penman–Monteith model（FPM） are extensively applied for vegetation evapotranspiration estimation because their reliability has been validated by many scholars. The Priestley–Taylor model（PT） and Hargreaves model（HS） require only the daily maximum temperature,daily minimum temperature and solar radiation to estimate evapotranspiration and are thus widely applied to grasslands but not to forests. We used the Energy Balance Bowen Ratio（EBBR） system to validate the accuracy of the four models. The results indicated that：（1） Compared to the EBBR measurement annual value, APM was the most accurate, followed by FPM, and PT;（2） During the year, the accuracies of the four models varied. APM and FPM underestimated evapotranspiration during June, July and August, whereas PT and HS overestimated evapotranspiration during this period. In the rest of the year, the estimation accuracies were reversed;（3） An analysis of the possible reasons indicated that wind speed, air temperature and precipitation were the most important contributors.High temperatures were measured in June, July and August, which led to an overestimation by PT and HS because these two models only calculated the temperature and radiation without vegetation information. Underestimation also occurred when a low temperature was recorded. Though APM and FPM addressed both meteorological and vegetation factors, slight deviations still existed; and（4） The two models were modified based on EBBR-measured data. Relative humidity was introduced into PT, and parameter ‘‘A’’ in the HS estimation model was amended to1.41. The accuracy of the modified models significantly increased. The study highlighted the application, comparison and improvement of four models in estimating evapotranspiration and offers more approaches to assess forest hydrological functions.

DETECTION OF FOREST FIRE IN DA HINGGAN LING REGION BY METEOROLOGICAL SATELLITE

From May 6 to June 2,1987,a huge forest fire broke out and raged for 28 days in Da Hinggan Ling region in far Northeast China,causing heavy loss of life and property,which claims the biggest forest fire disaster in Chinese history.The fire drew attention of the whole of China and was also concerned by many other countries.How were the meteorological satellites used in the detection of the forest fire?This paper elaborates the principles and methods of the fire detection using meteorological satellites,so that to sum up the experience and to increase the ability of forest fire detection.