<p>Freshwater availability in coastal areas depends on the withdrawal from tidal rivers and is severely threatened by saltwater intrusion, especially in the dry season. Freshwater availability is associated with natural factors and human activities. Although analyses of freshwater availability under saltwater intrusion is problematic, it has received limited attention in the literature. We propose a new framework, i.e. regulation by avoiding saltwater withdrawal (RASW), where the relationships among saltwater intrusion, upstream streamflow, and water supply are established, using hybrid data-driven method coupling wavelet transform and random forest, and considering data on streamflow, tide, wind, salinity of withdrawal stations, capacities of withdrawal projects and reservoirs, and water demand. RASW contains three phases, i.e. estuary salinity-exceedance simulation, upstream streamflow distribution design, and local water supply security analysis. The method is tested on the water supply for Zhuhai-Macao of the Guangdong-Hong Kong-Macao Great Bay Area, South China. Results demonstrate that the salinity-exceedance simulation model using a hybrid data-driven method is quite accurate. The meta-Gaussian copula efficiently simulates the six-dimensional distribution of upstream monthly streamflow and is appropriate for streamflow distribution scenario design. Water supply security benefits greatly from the joint river-reservoir regulation mode. But for a given exceedance frequency of average streamflow, the modes and security situations are diverse, due to various streamflow distributions, i.e. extremely low streamflow and its occurrence time. The proposed framework facilitates integrated decision-making for water supply security in coastal areas. Moreover, the capacities of facilities should be carefully considered according to local conditions, and streamflow distribution design can be utilized as a management tool to regulate water supply system. </p>

Abstract. Spatial and frequency distributions of precipitation should be considered in determining design water demand of irrigation for a large region. In Guangdong province, South China, as a study case, an eight-dimensional joint distribution of 10 precipitation for agricultural sub-regions was developed. A design procedure for water demand of irrigation for a given frequency of precipitation of the entire region was proposed. Water demands of irrigation in the entire region and its subregions using three design methods, i.e. equalized frequency (EF), typical year (TY) and most-likely weight function (MLW), were compared. Results demonstrated that the Gaussian copula efficiently fitted the high-dimensional joint distribution of eight sub-regional precipitation values. The Kendall frequency was better than the conventional joint frequency to analyze the 15 linkage between the frequency of the entire region and the joint frequency of sub-regions. For given frequencies of precipitation of the entire region, design water demands of irrigation of the entire region among the MLW, EF and TY methods slightly differed, but those of individual sub-regions of the MLW and TY methods fluctuated around the demand lines of the EF method. The alterations of design water demand in sub-regions were more complicated than those in the entire region. The design procedure using the MLW method in association with a high-dimensional copula, which simulated individual univariate 20 distributions, captured their dependences for multi-variables, and built a linkage between regional frequency and sub-regional frequency of precipitation, is recommended for design water demand of irrigation for a large region.

General comment The authors developed an eight-dimensional joint distribution of sub-regional precipitations using Gaussian copula, and proposed a design procedure for water demand of irrigation of a large region and provided three design methods, i.e. equalized frequency, typical year and most-likely weight function, to compare water demands of irrigation in the entire C1

In this paper, authors used the multivariate Gaussian copula and the general normal distribution to develop an eight-dimensional joint distribution of sub-regional precipitations. Using three design methods, i.e. equalized frequency, typical year and most-likely weight function, design combinations of sub-regional precipitation for a given cumulative frequency of entire regional precipitation were proposed and applied to analyze water demand of irrigation in a large region and its sub-regions. In a large region, design combinations of sub-regional water demand of irrigation were produced by the C1