Worldwide, decision-makers and non-government organizations are increasing their use of citizen volunteers to enhance their ability to monitor and manage natural resources, to conserve protected areas for example.

Citizen science (or, community science) is the process whereby simple citizens are involved in what is known as “science as researchers” [Kruger, 2000]: it is more than “scientists using citizens as data collectors”, but rather “citizens acting as scientists”. It offers important tools designed to facilitate the monitoring of common community [environmental] concern by simple citizens, government agencies, industry, academia, community groups, and local institutions, working together [Kruger, 2000]. Such community-based monitoring (CBM) initiatives include citizens and stakeholders in the management of natural resources and watersheds [Keough, 2006]. This is highly coupled with Integrated Water Resource Management (IWRM), which is regarded as “the process, which promotes the coordinated development and management of water, land and related resources, in order to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems” (www.gwpforum.org). This definition clearly states that water management is an interdisciplinary process, but also more importantly, decisions must involve the participation of members of the community affected by water-related strategies, in other words the stakeholders – that is to say the most affected members of the community, rather than just the most powerful and organized, or only the legally involved parties. 

In Europe, participation in water resource planning gained a new institutional stature with the Water Framework Directive (WFD). This calls for the active involvement of all interested parties in the implementation process and particularly in the production, revision, and updating of River Basin Management Plans (Article 14; Council of the European Communities, see [EC, 2000]). Planning methods that combine public participation with decision-making functions are therefore increasingly in demand [EC, 2002].

Citizen contributions can be successfully integrated in the field of water management. There are certain situations when it is difficult to collect accurate data, either due to a lack of sensors, or other data sources [Thaine, 2018]. In these situations it is possible to improve the processes of monitoring and modelling through the use of citizen data, collected either directly or through social networks. 

Such methods can be integrated at different levels in a project. At the simplest level citizens can be used only as sensors to collect data, while a more complex integration of citizen science is in the definition of the problem. At the next level of integration, citizens can also be involved in data analysis. This is the most complex participatory science level, where the volunteers are involved in the entire processing chain, for problem definition, data collection and analysis. 

For example, in the field of water management, such techniques can be used to determine water levels where there are no other data collection methods. In [Lowry, 2013] volunteers would send water gauge readings through text messages. 

Text messages were also collected to determine water levels by the authors of [Walker, 2016]. The same goal of determining water levels was also in [Starkey, 2017], but the collected data was also augmented with pictures and media collected from social media. Beside water levels, crowdsourcing can be also used for flood modelling. In this case, it is possible to determine different variables, such as: water level, velocity, land cover, topography [Thaine, 2018]. 

Beside the usual social media information sources, Youtube can also be used to determine water levels. The authors of [Michelsen, 2016] estimated water levels taken from images of the same area from youtube videos. The estimated values were accurate due to known elements in the area, such as walls with graffiti, while the time of the measurement was either the upload date of the video or the time reported by the uploaders, if it was present.

An interesting topic of the community science is coupling several data sources, at pan-European scale, from participatory actors. The design of effective indicators at a continental scale requires both conceptual and spatial aggregation (see Section 5.1).

Participatory research through partnerships between scientists and citizens provides an approach to natural resources management, which recognizes the complexity of issues with collecting enough data (see Section 5.2).

For data collection in particular, more recently people turned their attention towards participatory sensing. Unlike the traditional questionnaire-based collection processes, participatory sensing relies on electronic means widely available for collecting the data with the help of people (see Section 5.3). 

For encouraging participation, various reputation models have been proposed and used for participatory sensing (see Section 5.4).

A problem that arises from the crowd-sensing applications is maintaining the integrity of sensor data collected (see Section 5.5).