## 4 Conclusions  
The computations performed for this study demonstrate it is possible to develop an ANN model to simulate variation in HM concentrations in stormwater and meltwater. The model is innovative because it attempts to simulate different mechanisms that affect HM concentrations. The use of a single mathematical model for that purpose has not been reported in the literature so far.  
The computations show it is possible to simulate HM (Ni, Cd, Cu, Zn, Cr and Pb) concentrations in stormwater flowing from catchments with different types of land use. The ANN-based model employed to that end ensures satisfactory reliability. The results reported in the study demonstrate that HM concentrations in stormwater are affected by the physical and geographical characteristics of the catchment, and also by parameters describing atmospheric conditions and air quality. It is also shown that for heterogeneous catchments (as those investigated in the study), it is difficult to clearly specify key variables that decide the selected HM concentrations. To validate the ANN models developed for the study, it is necessary to conduct further field investigations.  
The methodology proposed in the study is universal in character. The analysis of spatial data making up the catchment characteristics, which are retrieved from available databases (orthoimagery, base maps, digital elevation models--[[http://www.gis.kielce.eu/](http://www.gis.kielce.eu/)]([http://www.gis.kielce.eu/](http://www.gis.kielce.eu/))), measurements of atmospheric conditions and air quality, (alternatively available monitoring network data--[[https://en.tutiempo.net/climate/poland](https://en.tutiempo.net/climate/poland)]([https://en.tutiempo.net/climate/poland](https://en.tutiempo.net/climate/poland)), [[http://smip.kielce.pios.gov.pl/](http://smip.kielce.pios.gov.pl/)]([http://smip.kielce.pios.gov.pl/](http://smip.kielce.pios.gov.pl/))) and measurements of HM concentrations in stormwater can be combined. That provides a tool which can be applied to model HM concentrations in different scenarios. The ANN method employed in the study is commonly used in computational packages. As a result, the development of the model and the optimisation of its structure are not complex tasks (the parameters are automatically estimated by the programs, e.g., MATLAB), and such an approach will gain in popularity in engineering practice. The model can be applied to spatial development and planning. It can be used to seek optimal solutions in stormwater management intended to reduce the HM content flowing from the catchment.  
Conceptualisation, B.S. and J.G.; methodology, B.S. and L.B.; validation, L.B. and K.G.; formal analysis, B.S.; investigation, L.B. and J.G.; resources, K.G.; data curation, B.S.; writing--original draft preparation, B.S., L.B. and J.G.; writing--review and editing, J.G. and K.G.; visualisation, L.B.; supervision, B.S.; project administration, L.B.; funding acquisition, J.G.  
This research was funded from the programme of the Minister of Science and Higher Education entitled \"Regional Initiative of Excellence\" in 2019-2022 project number 025/RID/2018/19 financing amount PLN 12,000,000\".  
The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.