Statistical evaluation of results of operative precipitation enhancement activities over large areas using historical regression method

Abstract

Review of methods, used for statistical evaluation of results of artificial precipitation enhancement activities, is given. The historical regression method, modified for statistical evaluation of results of operative works on the artificial precipitation enhancement over large areas, is described. To control the efficiency of operative works, the "floating control method," which uses a variable, or "floating," set of meteorological stations as control stations instead of the fixed one, is proposed to be used. Problems of the criterion choice and the best regression equation search procedure are considered. EVALUATION METHODS OF RESULTS OF ARTIFICIAL PRECIPITATIONENHANCEMENT ACTIVITIES The problem of evaluation of results of active influence on clouds has appeared since the first attempts of such influence. In so doing, the results of the stratus clouds' seeding, which do not produce the precipitation, could often be controlled visually or detected with the help of radar observations [2], but the effects of influence on convective clouds, especially under conditions of natural precipitation falling, are often veiled by processes of their natural evolution. Meanwhile, it is the influence, aimed at the intensification of processes of natural precipitation formation, that provides the obtaining of maximal absolute precipitation increment [1].The complication of the evaluation of active influence results is caused by large spatiotemporal variability of the majority of types of natural processes of precipitation formation, difficulty in the obtaining of their characteristics with accuracy and spatial and temporal resolution, which are necessary for the evaluation of influence results, as well as by the fact that influence effect does not usually exceed the amplitude of natural precipitation variations. On the other hand, in spite of this, in most cases the precipitation increments, induced by the influence, are of great economical importance, that increases still more the significance of the evaluation of efficiency of artificial influence on precipitation formation processes in cloud systems of various types.At the initial stage of works on the artificial precipitation enhancement one tried to obtain the influence efficiency evaluation by means of the comparison of precipitation, falling out during the influence period, with their climatic norm for this period [16]. Subsequently, such attempts have not become widespread, because it became clear that, due to the large natural precipitation variability, exceeding the influence effect by value, one should apply more sensitive methods to evaluate the efficiency. However, since the first works, the researchers paid attention to the close link of two problems, the evaluation of influence efficiency and the evaluation of natural precipitation amount, which could fall out in the case of the influence absence. It is obvious that the exact information on the amount of natural precipitation, which might fall out over the area under influence (target), could enable to determine ...

Evaluation of cloud seeding project in Yazd Province of Iran using historical regression method (case study: Yazd 1 cloud seeding project, 1999)

“…The period of cloud seeding activities may differ, in principle, from the preceding period, in particular, due to the change in frequency of various types of synoptic situations, which can be characterized by various regression coefficients between target and control area precipitation [17]. Another probability of the origin of differences, connected with time is possibly, the difference in microclimatic trends of target and control area precipitation, however the origin of the differential trend is unlikely in the case of the near location of the target and control area [2].…”

“…impact assessments of the cloud seeding were regarded from the initial seeding operations all around the world. The results derived through seeding of the stratus clouds that usually don't result in rainfall, are controllable by in situ observations or by using the radar based watch [2]. Whiles the impacts of convective cloud seeding, especially in the case of natural rainfall, often are hidden.…”

Advances in the Evaluation of Cloud Seeding: Statistical Evidence for the Enhancement of Precipitation

“…Reasonable estimation of the natural precipitation in the target area is a key point of statistical tests of artificial precipitation enhancement effect. Some experiments use precipitation in control area directly or use precipitation in control area as the predictor to establish a regression equation for the estimation (e.g., Guo, ; Jia, ; Jia et al, ; Koloskov, ; Kong & Shen, ; Li et al, ; Manton et al, ; Manton & Warren, ; Solak et al, ; Wang et al, , ; Wang & Yao, ; Yu et al, ). The prerequisite of the two methods is that the correlation of natural precipitation in the target area and the control area remains unchanged in both the seeded and unseeded periods.…”