Fig. 4: Trends in per capita gross leakage load under population and economic growth.

(a) Boxplot of the value and comparison of daily per capita gross leakage load (PL_gross) for Small cities, Middle cities, Large cities, and Megacities, with outliers defined as 1.5 times the interquartile range (IQR); (b) Trend plot of daily per capita gross leakage load (PL_gross) with increasing economic development, which is indicated by total nighttime lighting intensity (NTL) (nanoW cm⁻² sr⁻¹) for cities of different population size and fitted line, where k is the slope of the fitted line. City size categories based on urban population (Pu): Megacities (>5 million), Large cities (3–5 million), Middle cities (1–3 million), Small cities (<1 million). The size of the circle indicates the urban population of the city.