# Estimating Maize Yield from 2001 to 2019 in the North China Plain Using a Satellite-Based Method
## 3 Results
### The Pattern of the Summer Maize Yield's Spatial Distribution  
In this work, we converted the estimated GPP using the LUE model to the summer maize yield based on the corrected HI. Figure 10 shows the maize yield's spatial distribution, at the pixel scale, from 2001 to 2019. Generally, the estimated maize yield in the NCP region is mainly distributed between 5000-7000 kg/ha, accounting for 61.6%. There are a few pixels less than 1000 kg/ha or more than 11000 kg/ha. In addition, we compared the spatial distribution of the estimated and statistical yields. Figure 10,b shows the county-level spatial distribution of the mean statistical yield and the mean estimated yield from 2001 to 2019, demonstrating good consistency between the two and the accuracy of the model's estimated yield. The projected yields display a distribution pattern of high in the north and low in the south, similar to the statistical yields. Overall, HB and SD had greater maize mean yields than HN, AH, and JS. Moreover, they demonstrate the significant regional variation in the maize yield over the NCP. In certain areas, like Dezhou city in SD province, the maize mean yield estimations are greater than 7000 kg/ha or even exceed 8000 kg/ha, while in other areas, like the majority of the county-level administrative districts in AH and several county-level areas in western and southern HN province, they are less than 5000 kg/ha. Additionally, we subtracted the estimated yield from the statistical yield and discovered that the results were concentrated between \(-\)300 and 200 kg/ha. The difference between the statistical and estimated mean yield is particularly noticeable in areas with small and dispersed planting areas, like some counties in SD province and western HN province (Figure 10).  
We also investigated the spatial association between the yield distribution and climate factors, such as precipitation (pre), air temperature (T), and photosynthetically active radiation (PAR). Pre is mainly found in the southeast, gradually decreasing from southeast to northwest. From south to north, T declines. Although PAR is higher in the SD Peninsula, it does not vary significantly throughout the research area (Figure 8). The average maize yield's regional distribution pattern differs from that of Pre, T, or PAR. Irrigation can be an important factor in influencing maize yields in the NCP, especially in HB and western SD provinces. From previous studies, it can be concluded that the NCP area has a high proportion of crop irrigation [56; 57]. In addition, we averaged the irrigation water use data (IWU, driven by [PERSON] et al. [58]) during June-September from 2011 to 2018 and found  
Figure 7: Spatial distribution of the county-level statistics and estimates for the mean maize yield from 2001 to 2019. Here, (**a–c**) show the statistical, estimated yields for maize and the difference between them, respectively.  
that the maize yields were highly consistent with IWU in HB and western SD provinces, with a high yield in areas with high IWU and a poor yield in areas with low IWU.