Water level change of Lake Machang in eastern China 1 during the past 200 years 2

8 Lake Machang, which occupies an area of approximately 30 km 2 in Jining City of 9 eastern China, was a historical reservoir on the Grand Canal existing from early 15th 10 century to early 20th century. The premodern monthly water level observation of Lake 11 Machang commenced in 1814 AD and ended in 1902 AD. The available observation 12 data from the monthly records could cover 75.6% of the whole study period 1814-1912. 13 Although the water level was seemingly artificially intervened by human activities, 14 monthly and annual water level changes still correlated well with precipitation. That is, 15 climate is still the dominant factor of water level changes on seasonal and annual scales. 16 The flooding of the Yellow River in 1871 AD carried large amount of silt into Lake 17 Machang, which resulted in the rise of lake bed and reclamation initiated by local 18 residents. In particular, after the reclamation activity was officially approved in 1900 19 AD, Lake Machang was massively reclaimed and eventually dried up in the early 20th 20 century. 21

Asian monsoon type. The monthly average temperature varies from −2 °C in January 48 to 27 °C in July. The annual precipitation is around 700 mm and mainly occurs in 49 summer as monsoon precipitation (Shen et al., 2008). 50 The middle section of the Grand Canal was repaired and modified in 1411 AD, and 51 the channel of River Guang was also slightly modified. A group of reservoirs were 52 established along the canal to ensure the water supply of the Grand Canal (Zhu, 2014; 53 Fei et al., 2021). Water was collected in the reservoirs in every autumn when the 54 monsoon precipitation was over and supplied the canal in spring prior to the monsoon 55 precipitation came (Lu, 1775). 56 From the River Guang and a few small rivers, water was introduced into the Machang 57 area and collected into a new reservoir, named as Lake Machang (Yang, 1430; Figure   58 1). The official gazetteer recorded that the area was previously a horse pastureland; 59 therefore, the new shuigui (reservoir) was named Machang Hu 2 (Xu, 1859). In this 60 regard, the official documents indicated that Lake Machang appeared in 1411 AD.

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However, a poem indicates that a lake already existed in this area which could date 62 back to the early 14th century. The poem is entitled West Lake of Jizhou Prefecture 3 . It 63 reads, the lake is clean and vast, and I cannot see the shoreline 4 … The author LI Gang 64 was the mayor of Jizhou Prefecture in the period of 1324-1327 AD. Therefore, this 65 poem was probably written in 1324-1327 AD.

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The Grand Canal in China is a world heritage site, and it is one of the greatest 69 artificial waterways constructed in historical times in the world.   (Table 1). Notably, the water levels were not those of above sea level but the water The water level variability of Lake Machang was compared with precipitation on 98 monthly and annual levels.

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The average monthly water level variability of Lake Machang in the period of 1814- 5). We found that the monthly water level responded well with precipitation but with a 102 time-lag of 2 months. As we mentioned above, the water level of Lake Machang as a 103 reservoir was artificially intervened due to human activities. Water was collected in 104 autumn and discharged into the canal when needed. This condition possibly explained 105 the time-lag of monthly water level variability.

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The annual water level variability of Lake Machang was compared with the Dryness 107 Wetness Index (DWI hereinafter) dataset described in the Central Meteorological  (Table 1) Figure 7). Lake Machang was drawn as a dry lake in this map. In 1927 AD, Lake 184 Machang was also drawn as a dry lake in the local gazetteer of Jining (Yuan, 1927). 185 From this maps, it could easily conclude that Lake Machang dried up no later than 1916. 186 Notably, the annual precipitation did not decrease significantly in the early 20th century.  were made in the four reservoirs. The average annual mean water level change of Lake 203 Nansi was calculated and compared with that Lake Machang over the period of 1814-204 1902 AD. The correlation coefficient is 0.374 (N=89) (Figure 6). The annual water level 205 change of Lake Machang showed great similarity to those of its neighbor reservoirs.

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On the contrary, the long-term evolution of Lake Machang and Lake Nansi were very 207 different. Lake Machang was reclaimed and dried up in the early 20th century, but Lake 208 Nansi gradually expanded (Fei et al., 2021). Lake Nansi was even more frequently

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From the perspective of geomorphology, the altitude of Lake Machang is a little 213 higher than that of Lake Nansi, and the Grand Canal in this region flows southeastward.

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That is, water flew from Lake Machang to Lake Nansi along the Grand Canal. When 215 Lake Machang was reclaimed, water that could otherwise be collected in it directly flew 216 into Lake Nansi, and resulted the expansion of Lake Nansi. Geologically, the basin of 217 Lake Nansi is slowly subsiding, whereas that of Lake Machang is stable (Shen et al.,      Lakes and Swamps (Pan, 1916)" (upper part). Enlarged image of the area near Lake Machang (lower 340 part). Lake Machang was drawn as a "dry lake" in this map.