Researchers at the Cold and Arid Regions Environmental and Engineering Research Institute, a part of the Chinese Academy of Sciences, have compared out a close association between the upper reach inflows of the Yellow River and sunspot activities. Researchers worked out the findings using two groups of data: flow charts of Tangnaihai, an upper reach site of the Yellow River since 1736, and the SCL variation curves of sunspots since 1734. Comparative studies show that the beginning of the dry period of the site is very close to the extremely short SCL years of sunspots.

The Longyangxia Reservoir, with a volume of 24.6 billion m³, is a reservoir sitting at the head of the Yellow River, capable to house a year's inflow from the upper reaches. Tangnaihai, a water flow measuring station monitoring the inflow into the Longyangxia Reservoir, reflects important information on the inflow from the upper reaches of the Yellow River through its own variations. In the past 270 years, sunspots have experienced 9 extremely long years, and 8 extremely short years. The site enjoys a wet year in each extremely long SCL year, while deploring for a dry year around each extremely short SCL year.

Research findings indicate that extremely long and short SCL years are desirable indicators to predict wet and dry years over the upper reaches of the Yellow River.  Physical measurements at Tangnaihai confirm that 1994-2004 makes the latest dry year period that lasts for 11 years, also the longest one. The latest extremely short SCL year started from 1996. The first half of 2005 data show that the inflow of the upper reaches of the Yellow River has approached a normal year level, which makes researchers believe that the dry year period will soon come to an end. The upper reaches will turn for wet years through an interval of several normal years.