New algorithm corrects misclassification of precipitation on the Tibetan Plateau

Like many natural phenomena, precipitation can be both a blessing and a curse on human life: on the one hand, it provides water for rivers and fields, but on the other hand, it can cause floods, landslides and other natural disasters. Either way, understanding and predicting the different types of precipitation is essential.

Collecting and analyzing precipitation data is important, but there are several places on Earth where this is difficult, one of which is the Tibetan Plateau, whose unique and challenging physical environment makes observing precipitation from above, either on the ground or via satellite, a challenging proposition.

As for satellite-based precipitation radar, the high altitude of the Tibetan Plateau often leads to misidentification of the type of precipitation, especially weak convective precipitation can be misidentified as stratiform precipitation because the height of the plateau terrain is close to the freezing point of the atmosphere in other areas.

Recognizing this, Professor Fu Yunfei of the University of Science and Technology of China (USTC) along with his colleagues from the China Meteorological Administration, in a study recently published in the journal Advances in Atmospheric Sciences, first conducted an in-depth analysis of the problems with the space-based precipitation radar’s existing precipitation type identification algorithm, revealed why the algorithm fails to identify precipitation types over the Tibetan Plateau in summer, and then developed and tested a new algorithm.

“In nature, there seems to be a tendency to standardize everything while ignoring the obvious complexities and diversity that exist at different scales,” Hu explains. “This is also true in our scientific field, meteorology. And when it comes to the specific problem we are trying to solve in this study, a concrete example is the thresholds adopted to identify precipitation types.”

Traditionally, classification methods for observation-based precipitation in non-plateau regions have been simplistic, resulting in a somewhat binary approach where precipitation is identified as either convective or stratiform.

The new algorithm developed by Fu’s team takes into account parameters such as maximum reflectivity, background maximum reflectivity, and echo-top height in more detail, resulting in a more detailed classification (types include “strong convection”, “weak convection”, “weak” and “other”), significantly reducing identification errors and providing more useful information.

Ultimately, Hu and his team’s work could be passed on to the weather forecasting and modeling community and adopted to better predict the occurrence of different types of precipitation events in parts of the world where existing standardized methods are less applicable. More specifically, as highlighted in the context of this particular paper, communities living in mountainous regions such as the Tibetan Plateau could feel great benefit.

“But I have to say there is still a lot to be done,” Fu concluded. “In particular, we need to confirm the existence of stratiform precipitation over the Tibetan Plateau in summer, which is still difficult to detect with space-based precipitation radar measurements for a variety of reasons. This will be the next step in our research.”

The paper appears on the cover of the issue of Advances in Atmospheric Sciences. The cover photo, taken by Fu in the Lianbao-Yeze Nature Reserve on the border of Xichuan, Gansu, and Qinghai provinces at over 4,000 meters above sea level, shows convective clouds over the lake in the foreground and on the far edge of the mountain in the center.